INTRODUCTION
This manual describes the logical structure and operation of the
English Electric DEUCE Computer. This is a high-speed general-purpose
electronic digital computer.
The individual circuits and other parts of the DEUCE are described
only in terms of their functions and of the sequence of signals passing
between them. Only indirect and occasional reference is made to the
operation of the electronic circuits as such.
The reader is assumed to be familiar with the notation of repres-
enting positive and negative binary numbers within the computer. Reference
is made to the section of the DEUCE Programming Manual describing this
notation.
Modified or additional sections of this manual will be issued from
time to time to keep it up to date with the continuing programme of
improvements to the facilities and operation of the computer.
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INDEX
CHAPTER TITLE PAGE
1 Brief General Description 1
2 Main Component Parts 12
3 Logical Diagrams 14
4 Fundamental Waveforms 19
5 The Circulation Unit 23
6 Control 26
7 Destination Triggers 47
8 Logical Operations Unit 49
9 The Adder 51
10 The Multiplier-Divider Unit 55
11 The Magnetic Store 87
12 The Reader and Punch 98
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BRIEF GENERAL DESCRIPTION
The operation Of the DEUCE will first be described as a whole, with
reference to most of its essential parts, before each part is described
in detail. In this rapid preliminary survey, a number of difficulties
will necessarily be glossed over, it is thought worth while, however, to
give the reader as quickly as possible a general framework into which
subsequent details can be fitted.
REPRESENTATION OF NUMBERS AND INSTRUCTIONS
Within the computer a number is represented, in binary form, by a
sequence of electric pulses, at intervals of 1 microsec, occupying 32
microsec in all. There are in general less than 32 pulses, since each
pulse represents a digit "1" in the number and a digit "0" is denoted by
a vacant microsec In which no pulse occurs. The least significant digit
always comes first.
Thus the number "13"; would be represented in 32 microsec at any
point in the Machine by a pulse in the first, third and fourth microsec
and the absence of pulses in the second, fifth and subsequent microsec.
The significance of the three pulses present is respectively 20 = 1,
22 = 4 and 23 = 8.
The same type of signal, consisting of 32 pulses and spaces at 1
microsec intervals, is also used to represent an instruction. This means
that the same storage mechanism can be used for either numbers or
instructions, and that an instruction can be modified, if required, by
the normal arithmetic units. For this reason, a common name is required
for any sequence of 32 digits which may be either a number or an instruc-
tion; the name chosen for this purpose is "word".
DELAY LINE STORAGE
The main type of storage unit is founded on a delay element which
after a constant delay reproduces at its output terminal any, signal
applied to its input terminal. In the simplest case, the delay is 32
microsec. Such an element is shown in Figure 1.1 with switches for
input and output. Suppose that switch D is opened to connect the input
with the delay, a single pulse is applied to the input and enters the
delay, and switch D is immediately closed. The pulse will travel along
the delay, emerge at B 32, microsec later and immediately return to point
A via switch D. It will then retraverse the delay and appear at B after
a further 32 microsec. This process is repeated indefinitely, provided
switch D is not disturbed; a single pulse appears regularly at B, once
every 32 microsec. In effect, a word has been stored which consists of
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a single "1" and 31 zeros. Any other pattern could equally well have
been stored, since the successive digits would follow each other through
the delay and emerge in their proper order.
To store a particular word, its successive digits are applied at the
input, switch D in opened and the digits flow into the delay; after 32
microsecs the last digit has just entered the delay and the first is about
to emerge; at this moment, switch D is closed to complete the circulation
path. The successive digits as they emerge at B are transmitted back to
A and re-enter the delay; no more digits are accepted from the input.
Any word previously stored in the system has now been lost, since the
circulation path was broken during the process of introducing the new one.
A copy of the word currently being stored may at any time be obtained at
the output simply by operating switch S. Switch D is known as the
"Destination Gate", switch S as the "Source Gate".
MINOR CYCLES
It will be observed that the word is stored like a whiting; it
appears repeatedly at point B, its last digit always being immediately
followed by its first. There is thus no indication in the stored digits
of where the word begins and ends. The Operation of the DEUCE is con-
trolled by a sequence of short pulses which occur incessantly at intervals
of 32 microsec; every operation begins at one of these pulses and ends at
another. The period of 32 microsec between two successive control pulses
is called a "minor cycle" (abbreviated "m.c.") The 32 digits of a word
which are applied to A during one minor cycle, appear at B during the
next; thus a control pulse always marks the moment when one word has
just ended and the next (or a repeat of the same one) is about to begin.
LONGER DELAY LINES
In the same way that 32 digits are stored in a delay element of 32
microsec, 1024 digits may be stored in a delay element of 1024 microsec.
These 1024 digits are generally regarded as making up 32 words of 32
digits each; this longer delay thus provides 32 storage positions for
single words. These words appear in rotation at the output in succes-
sive minor cycles; to keep track of them the minor cycles are numbered
from 0 to 31 and then starting again at 0. A sequence of 32 minor cycles
is called a "Major Cycle". It is clear that a word which emerges from
the delay in minor cycle 5 of some Major Cycle will reappear in m.c. 5
of the next and every subsequent Major Cycle until it is replaced with
another word. The word is said to be stored in m.c. 5 (of this Delay
Line). To replace this word with a new one without affecting the contents
of any other minor cycle. the Destination Gate must be opened only during
m.c. 5; also, the new word to be stored must he presented at the input
during this minor cycle, whether or not it is repeated in the previous
and succeeding minor cycles. For every minor cycle in which the
Destination Gate is open, the word previously stored will be replaced by
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the word then being applied to the input. The timing of the Destination
Gate must therefore be closely controlled; a special signal is supplied
for this purpose. It will be seen, however, that the timing requirement
for the Source Gate is far less stringent.
LAYOUT OF DELAY LINE STORE
The DEUCE storage system includes twelve of these 1024 microsec
delay lines, four of 32 microsec each and also three of 64 microsec for
two words each and two of 128 microsec for four words each. The delay
lines are numbered from 0 to 21, and each number is prefixed by a two-
letter code which indicates the storage capacity. The complete layout
is as follows:
Delay Words Stored Name Number References
1024 microsec 32 each "Delay Line" 12 DL1 to DL12
32 microsec 1 each "Temporary Store" 4 TS13 to TS16
128 microsec 4 each "Quadruple Store" 2 QS17 and QS18
64 microsec 2 each "Double Store" 3 DS19,DS20,DS21
NOTATION FOR QS AND DS STORAGE
The four words in a QS are said to be stored in minor cycles 0, 1, 2
and 3. though the word in m.c. 3, for instance, emerges not only in m.c.3
but in m.c. 7, 11, 15 ... 27 and 31. It may be used or replaced in any
of these minor cycles. The word emerging from QS 17 in m.c. 3 is said
to be stored in 173; this notation is used for all DL, QS and DS, though
the range of numbers appearing as the suffix is different in the three
cases. The two minor cycles of a DS are numbered "2" and "3" rather than
"0" and "1"; this is to avoid confusion with the "0" meaning "odd minor
cycle".
Comparing a DL with a TS it will be seen that the DL has the advan-
tage of storing 32 times as much information with very little extra
equipment; on the other hand, a given one of the 32 words stored is
available for use or replacement only once in a Major Cycle instead of in
every minor cycle. By using a range of TS, DS, QS and DL it is intended
to have the best of both worlds, very rapid access to the words in imme-
diate use combined with economy of storage equipment. This principle
will be discussed further when we come to consider the Magnetic Store and
its relation with the Delay Line store.
INTERCONNECTIONS IN THE DELAY LINE STORE
Figure 1.2 shows DL1, DL2, TS13 and TS14, with their common connec-
tions. The common connection of all Input and Output points is called
the Highway. The process will be described of transferring a word from
one position to another within this elementary store. It will not yet
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be clear why this procedure is in any way useful, but we will let that
pass for the moment.
To replace the word in TS13 with a copy of that in TS14, the first
thing is to open S14; repeated copies of the word in TS14 flow through
the Highway and appear at all the Destination Gates. D13 is now opened;
the word on Highway flows into TS13, while the old word in TS13 is lost,
digit by digit, as it emerges from the delay. After 32 microsec (or more,
it does not matter in this case) D13 is closed, trapping the word from
TS14 in TS13.
The Computer is now free to proceed to its next operation. This might
be to replace the word in 27 with a copy of that in 14. The procedure is
the same, except that in this case it is essential for D2 to be opened
sharply at the beginning of m.c. 7 and closed equally suddenly at the
end. Otherwise, more than one word in DL2 will be replaced with copies
of the one in TS14.
To replace the word in 27 with a copy at that in 17, S1 may be
opened at any time; it is again essential for D2 to be opened only
during m.c. 7.
A direct transfer is impossible from, say, 112 to 27; this process
can be effected only in two stages, transferring first from 112 to any
idle TS and then from there to 2. Similarly, direct transfers cannot
take place from (DS) 192 to (DS) 213 , to (QS) 171, or to any odd minor
cycle in a DL, or from (QS) 183 to 192, to 171,or to any minor cycle of
a DL other than m.c. 3, 7, 11, 15, 19, 23, 27 or 31.
Incidentally, transfers are possible which last for any integral
number of minor cycles up to 32. This timing, of course, refers to the
opening of the Destination Gate for the relevant period; the Source Gate
is always opened for a period which overlaps this at both ends. For
instance, one may in one operation replace the words in DL1 m.c. 21 to 24
either with four copies of the word in TS16, with two copies each of the
two words in DS20, with one copy each of the four words in QS18 or with
the four words in DL2 m.c. 21 to 24.
OTHER SOURCES AND DESTINATIONS
The DEUCE works by carrying out a sequence of transfers in a pre-
Determined order. For each transfer, the Source and Destination numbers
must be specified, as well as the minor cycle or sequence of minor
cycles for which Transfer is to take place. There are 32 Sources and 32
Destinations, each numbered from 0 to 31. 21 Sources and 21 Destinations
are associated with the different storage positions. The other 11 of
each are connected to various pieces of equipment for doing arithmetic
operations and controlling the input and output devices. In these cases,
there is no particular relationship between the Source and Destination
bearing the same number.
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In the usual abbreviation, a transfer from S14 to D13 for example is
Written "14-13". Where a DL is involved, the minor cycles of operation
Must also be specified as in "4-7 (m.c. 14, 15 and 16)". In some cases,
only the number of m.c. is relevant; "18-17 (4 m.c.)" replaces all four
words in QS17 with copies of those on QS18; this is not affected by
which four minor cycles are used for the transfer, and it could, in fact,
go on for more than four minor cycles without further effect.
INSTRUCTIONS
Each transfer is specified by an "Instruction"; this is a word of
32 digits coded in a special way to represent the required transfer. The
precise form of coding will be described later; it will suffice for the
moment to say that any of the transfers mentioned as examples are capable
of being represented by an Instruction within this code.
CONTROL MECHANISM
There is a part of the DEUCE called "Control" whose function is to
interpret Instructions from the coded form and make the necessary
connections for them to be obeyed. Instructions to be obeyed are nor-
mally stored in the Delay Line store; the Control incorporates a special
storage line, TS COUNT, in which is held the Instruction currently being
obeyed. The pattern of operation is to take an Instruction into TS COUNT,
set up the necessary connections and obey it, and then take in the next
Instruction. Since the computation performed is determined as much by the
sequence in which Instructions are obeyed as by the individual Instruc-
tions themselves, it is arranged for each Instruction to specify, as well
as the Source. Destination and minor cycle or cycles of transfer, the
storage location of its successor.
INSTRUCTION HIGHWAY
There are two entrances by which a word may reach Control to be
obeyed as an Instruction. The usual one is available only to words
stored in one of the first eight DLs (DL1 to DL8 inclusive), a maximum
total of 256 words. Each of these DLs has, as well as its Scores and
Destination Gates, an extra gate called its "Next Instruction Source
Gate". These are numbered from 0 to 7, numbers 1 to 7 referring to the
corresponding DL and number 0 referring to DL8. These eight "NIS" Gates
lead, not on to the main Highway, but on to a special "Instruction High-
way" (IHW) which leads in turn to Control. The connections for DLs 1, 2
and 8 are shown in Figure 1.3. By opening only the NIS Gate specified
in the current Instruction, Control ensures that the next Instruction
will come from the required DL. There remains the timing problem of
picking out from IHW the correct one of the 32 words in that DL. This is
solved by admitting the IHW signal into TS COUNT through a special gate
which is opened only for the minor cycle in which the required new
Instruction word is emerging from its DL of residence.
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The second entrance to Control is described in the next paragraph
but one.
TIMING SIGNALS
Control is thus required to generate two timing signals. One opens
the selected Destination Gate and thus controls the main Transfer Timing;
this signal is called Transtim or TT. The other opens the gate into TS
COUNT and thus controls the Timing at which Control takes in the new
Instruction; it is called Timci or TCI.
The only other signals emerging from Control are the three sets of
Selection signals, one set each for Source, Destination and Next Instruc-
tion Source.
DESTINATION "0"
The other entrance to Control is through a special Destination Gate
which has been given the number "0". Operation of this gate usurps the
IHW connection to TS COUNT and replaces it with a connection from the
main Highway. Thus by this means it is possible to inject into TS COUNT
as an Instruction any word which is available at a Source. For instance,
the Instruction "13-0" takes as its next Instruction the word currently
stored in TS13. The connections are shown in Figure 1.4. It will be
seen that a word from HW transferred to D0 has still to pass through the
TCI gate; this means that both TCI and TT signals must be present
simultaneously for the Instruction to take effect.
DISCRIMINATION
It frequently occurs in the course of a computation that what is to
be done next depends on what has already happened. Reduced to its
essentials this requires the existence of an Instruction which is capable
of being followed by either of two successors depending, in some sense,
on "circumstances". This requirement is met by two special Destinations
D27 and D28. An Instruction which transfers a number to one of these
Destinations picks its succeeding Instruction word from either of two
Locations (in practice, adjacent minor cycles of the same DL) depending
on some characteristic of the number transferred. D27 discriminates
between positive and negative numbers, D28 between zero and non-zero
numbers. For example, which of two possible Instructions comes next
after "13-27" depends on the sign of the number in TS13. D27 and D28
work by modifying the TCI Gate timing signal, and therefore form part of
Control. Figure 1.5 shows the Control as a block with all its input
and output connections.
ARITHMETIC OPERATIONS
An essential function of a Computer is to carry out some selection
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of arithmetic operations. In the DEUCE, this is achieved with the same
"transfer" type of operation by giving special facilities to certain of
the Sources and Destinations. Each of these arithmetic Sources and
Destinations is associated with a particular TS or DS (sometimes with
two, as in the case of multiplication where a TS is used to store the
multiplicand and a DS holds the multiplier at the beginning and the
double-length product at the end of the operation. But this is compli-
cated - we will start with a simpler example).
ADDITION
Addition may be performed by using D25, which is associated with
TS13. The arrangement is shown in Figure 1.6. The function of the box
Marked "+" is to add together the two numbers applied at the input
Terminals A and B and to present the sum of the two at the output
terminal C. It will be appreciated that the two sequences of pulses and
spaces at A and B may be taken to represent two binary numbers, that these
two binary numbers have a unique binary sum, and that this binary sum can
in turn be uniquely expressed as a sequence of pulses and spaces. This
is the output signal produced by the "+" box or "Adder".
If D25 is not being used, the signal at A always represents the
number zero; the signals at C and B are then identical and TS13 acts as a
simple storage position for all purposes, the Adder appearing as a short-
circuit between B and C. When a transfer is made to D25, the number or
numbers transferred are added to the previous contents of TS13. A few
examples of such transfers will be given. "14-25" replaces the number in
TS13 with the sum of those previously in TS13 and TS14 (TS14, of course,
remains unchanged). "14-25 (3 m.c.)" adds three times the number in TS14
to that previously in TS13. "13-25" doubles the number in TS13 or, to
put it another way, shifts the number in TS13 up by one binary place.
"13-25 (5 m.c.)" gives a shift up of five binary places. "1-25 (32 m.c.)"
adds the 32 numbers in DL1 together into TS13. It will be observed that
D25 and D13 cannot both be used at once; an Instruction contains only
one Destination number.
ARITHMETIC SOURCES
Several Source numbers are allocated to arithmetic operations. As
in the case of arithmetic Destinations, only one example will be given
at the moment. We have seen how to shift a number upwards by putting it
in TS13 and using D25. A number may be shifted downwards by putting it
in TS14 and using S23. The connections are shown in Figure 1.7. The
box "L" has one input at A and two outputs at B and C. That at B is
identical with the input, that at C represents the input number divided
by two, that is shifted down by one binary place. The Instruction
"23-14 (6 m.c.)" has the effect of shifting the number in TS14 down by
six binary places.
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FIXED NUMBERS
Certain useful fixed binary configurations are permanently available
At Sources. These include "all zeros" at S30, "all ones" at S31 and at
S27 a configuration containing a single "1" in the least significant
position. This last in called "P1". The Instruction "27-25" adds one
to the number in TS13. The method of generating P1 will be described
later; for the present the notation of Figure 1.8 will be used.
INPUT AND OUTPUT
Numbers and Instructions reach the Machine from outside by being
injected on to Highway through Source 0. In the course of a computation,
the Computer assimilates new information when required (either more data
or further Instructions) by obeying an Instruction with Source number "0",
which has been included in the program. To get started in the first
place, a key is pressed which clears the whole Delay Line Store; this
leaves to be obeyed the Instruction "0-0", which has the effect of
reading a single (Instruction) word from the Input to TS COUNT. This
single spy is used to call in a platoon, a company and finally the big
battalions.
Calculated results are sent out from Highway through D29. A
schematic of SO and D29 is given in Figure 1.9 for the sake of complete-
ness rather than explanation. Input and Output, by the way, is always
in signal notes. The Instruction "0-4 (m.c. 7)" sends the word currently
at the Input to 47; "14-29" sends the word in TS14 to the output. These
few notes on Input and Output have no doubt raised more questions than
they have answered; these will be dealt with, it is hoped, in later
sections of this report.
DESTINATION "TRIGGERS"
All the operations so far described have had some genuine element of
"transfer" in the sense that digits flowed from one part of the Machine to
another. There remain some cases, however, in which this is not true.
The problem is to fit these into the "Source and Destination" framework
so that the same form of Instruction word can be used. One special
Destination is therefore allotted jointly to all these operations which
lack the "transfer" element; this is D24, called "Destination Triggers".
There are about a dozen of these operations altogether, each of which is
specified by a particular Source number used in conjunction with D24;
a few examples will be given.
Information normally comes into the DEUCE punched on Hollerith cards
which pass successively through a Reading machine in response to a demand
from the Computer. This demand is the Instruction "12-24" which causes
a sequence of cards to start passing through the Reader; the flow may
be stopped at any time by the Instruction "9-24". Output of information
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is through a Punching machine which is fed with a supply of clean cards;
the Punch in started by "10-24" and stopped by "9-24". The same
Instruction is used to stop either the Reader or the Punch because they
are never in practice used at the same time.
The DEUCE contains an automatic Multiplier and an automatic
Divider; operation of these is initiated respectively by "0-24" and
"1-24". In these cases there is no corresponding stopping Instruction,
since both circuits are arranged to stop themselves automatically as soon
as the arithmetic operation is complete.
Figure 1.10 shows the D24 connections. It will be seen that there
is no concoction with Highway; this permits the dual function of the
Source selector. Obeying an Instruction with Source number 12, for
example, means both that the contents of DL12 will appear on Highway and
that if the Destination number is 24 the Reader will be started; in the
latter case, the contents of Highway is irrelevant, since none of the
Destination gates connected to it is open. The two "switches" labelled
"S12", for example; one connected to Highway and one to Destination
Triggers; actually represent two separate electronic gating circuits
operated by the same control signal.
THE MULTIPLIER
The operations of multiplication and division are somewhat different
from the arithmetic operations so far described. Only the Multiplier
operation will be described at present, since that of the Divider is
similar. A Multiplication requires several Instructions; first the two
factors must be sent to particular storage positions, the multiplicand
to TS16 and the multiplier to DS213. Next, DS212 must be cleared. Now
we are ready. The Multiplier is brought into action by obeying the
Instruction "0-24", which uses Destination Triggers. After 65 minor
cycles, multiplication is complete, and the product, which comprises 64
digits, remains in DS21. The multiplier has been lost but the multipli-
cand remains in TS16. The Multiplying circuit automatically switches
itself off 65 m.c. after the start. Figure 1.11 shows a schematic of the
system.
MAGNETIC STORE
As well as the Delay Line Store, the DEUCE has an auxiliary store,
called the Magnetic Store, for about 8000 words. This is much larger
than the Delay Line Store, but the information takes a longer time to
get into and out of it. The Magnetic Store works by taking information
from the Delay Line Store, holding it, and returning it later when it is
wanted.
Information is transferred in either direction, always in blocks of
32 words, and always to or from DL11. In other words, the two operations
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in which the Magnetic Store is concerned are to transfer the whole
contents of DL11 into the Magnetics and to transfer a clock of 32 words
from the Magnetics into DL11. Two special Destinations, D30 and D31 are
allocated the job of initiating these "Magnetic Transfers". Figure 1.12
shows the system, only one Magnetic Control Destination, i.e. D30, being
shown.
MAIN SCHEMATIC OF THE DEUCE
We are now in a position to assemble the various components so far
Described into a coherent whole. Figure 1.13 is a schematic of the whole
machine. For the sake of simplicity, only one or two examples have been
included from each group of parts of a similar type; for example, from
the group of five Sources S27(P1), S23(P17), S29(P32), S30(Zeros) and
S31(Ones), only the first is explicitly shown in the figure.
We will trace through the successive operations of "obeying an
Instruction". Suppose the Instruction enters TS COUNT in minor cycle "m".
In m.c. (m+1) it first enters the main part of Control and the three
selectors are set up; nothing else happens in this minor cycle, which is
therefore known as the "set-up" minor cycle. The Source and NIS selection
take immediate effect, in the sense that digits from the selected Source
immediately begin to flow into Highway and that digits from the selected
NIS immediately begin to flow Into IHW. The Destination selection does
not take effect until Transtim signal is supplied.
The transfer specified by the Instruction may commence with any
minor cycle from (m+2) to (m+33) and may continue for any integral number
of minor cycles from 1 to 32. Thus after the set-up minor cycle there is
a pause of from 0 to 31 m.c. as specified in the Instruction; then
Transtim signal is applied for a period of from 1 to 32 m.c. and
"transfer" takes place for this period. This "transfer" may be a simple
transfer of words between sections of the Delay Line Store; it may be
an addition in TS13 or a shift in TS14, it may be the initiation of a
multiplication or division, of a passage of cards through the Reader or
Punch, or of a Magnetic Transfer; it may be the transfer of a word from
the input or to the output; it may be the insertion of a number into the
Discrimination circuits to determine, according to its sign, the
selection of the next Instruction; it may be the direct insertion into
TS COUNT of a word which has been built up in a TS by arithmetic action
and is now required to be obeyed as an Instruction. Which, of all these,
is determined by the particular Source and Destination numbers speci-
fied in the instruction.
For all this time, the successive words in the DL whose NIS has been
Selected have been flowing into IHW and presenting themselves in turn
at the TCI gate into TS COUNT. Once the transfer has been completed and
Transtim removed, TCI signal is supplied for that single minor cycle in
which the required next Instruction emerges from this D.L. Thus the next
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Instruction gets into TS COUNT and the cycle of operation begins again.
Since the new Instruction passes once through TS COUNT before it reaches
the main part of Control to take effect, it may actually be admitted to
TS COUNT during the last minor cycle of Transtim, though never, of
course, any earlier. This enables a minor cycle to be saved in the
operation time of a large number of Instructions, and is essential in any
transfer to D0.
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MAIN COMPONENT PARTS
In physical form, the DEUCE may be said to consist of six main parts
Joined together by electrical connections, though two of them are also
joined together physically. They are the Main Frame, the Control Panel,
the Reader, the Punch, the Delay Line Store and the Power Unit.
READER AND PUNCH
The main input and output of information, including the input of the
Program, is by Hollerith cards. The DEUCE must therefore incorporate
devices for reading and punching these cards. In each case, a standard
piece of Hollerith machinery has been modified by replacing its electric
circuits with relay mechanisms which link its operation with that of the
Computer. The Reader is made from a Balancing Tabulator, the Punch from
a Gang Punch. Both are joined with the rest of the DEUCE by cables.
MAIN FRAME
The electronic circuits comprise about 1450 valves with their
Associated components. These are mounted in about 68 chassis each of
which has 20 or 30 valves. A chassis consists of a more or less flat
plate with the valves sticking out on one side and the components
mounted on the other. The individual chassis are mounted in a Main
Frame which consists of nine vertical racks solidly mounted together,
each capable of holding eight chassis.
Each chassis is a self-contained unit, connected to the Main Frame
by a pair of plugs and held in place by two bolts. One of the plugs
carries the power supplies which are in a standard arrangement for all
chassis; the other carries the signal connections between chassis. Most
chassis are individual and not like any other, but there are a few groups
of identical chassis. For instance, the gates and some of the amplifiers
associated with a delay line storage position are made up into a standard
chassis called a Circulation Unit. There are, of course, 22 copies of
this chassis in the machine, one for each storage location including
TS COUNT.
The Magnetic Storage Drum is also mounted in the Main Frame on a
special chassis not of the standard shape.
POWER UNIT
The Power Unit takes in a three-phase mains supply and produces all
the d.c. and a.c. voltages required by the rest of the DEUCE. There are
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seven d.c. lines to the Main Frame, -300v, -200v, -100v, earth, +100v,
+200v and +300v. Special d. c. supplies are also required for the Reader
and Punch and for the relays in the Control Panel. Valve heater supplies
are generated by transformers mounted on the Main Frame fed with a.c.
mains voltage from the Power Unit. The mains switching is done by
contactors operated with buttons; a duplicate set of buttons is mounted
on the Control Panel.
DELAY LINE STORE
The twelve long delay lines of 1024 microsec each are mounted in a
Small thermostatic chamber connected by cables to the Main Frame. Above
the periphery of the upper part of the chamber are mounted a pair of
amplifiers to each DL, one power amplifier for the input signal, one
high gain amplifier for the output signal. The complete unit is capped
by an overhanging lid giving the appearance of a mushroom.
CONTROL PANEL
The Control Panel, which is mounted on the main frame, carries a
Multiplicity of keys, buttons, lamps and monitors which are not used much
when the DEUCE is working normally on computation. The Control Panel
comes into its own in investigating faults in the operation of the
Computer and when testing and correcting the operation of a new program.
The Control Panel carries a row of 32 keys for the input of single
numbers and a row of 32 lamps for the output of single numbers, an alarum
buzzer and lamp to indicate the failure of an internal check in the
program, two monitor cathode-ray tubes for displaying the contents of
the various delay line storage positions, and keys for imitating almost
everything that the DEUCE normally does automatically. For instance,
there is a key labelled Transtim which, when pressed, gives continuous
transfer between whatever source and destination are selected; another
key, labelled TCI gives, when pressed, continuous entry to TS COUNT for
the words on IHW. Pressing a key called External Tree overrides the NIS,
S and D parts of the word in TS COUNT and replaces them with the con-
figuration set up on a row of 13 keys (one for each digit) also mounted
on the Control Panel.
There are keys for specifying the result of a discrimination indep-
endently of the number transferred, for starting and stopping the Punch
or Reader and for many other purposes. When considering the detailed
operation of the Machine, we shall frequently come across signal lines
to and from the Control Panel which have no part in the normal operation
and are used only for usurping the normal arrangements in time of
emergency.
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LOGICAL DIAGRAMS
Having put the DEUCE together as rapidly as possible, we may now
take it apart at our leisure and examine the component sections. Before
doing so we must expand one of two of the many over-simplifications in
the preceding paragraphs and introduce the notation which will be used to
describe the operation in detail.
WIDE AND NARROW PULSES
Within the Computer, the pulse interval is always 1 microsec, but the
width of the pulse representing a digit "1" may take either of two values,
depending on the point in the Machine at which the pulse train appears.
(a) Narrow Pulses
Pulse width about 0.3 microsec. There is a clear gap between
two pulses representing adjacent "1"s. This type of signal may
be fed through an a. c. coupling, and is mainly used in connec-
tions between units.
(b) Wide Pulses
Pulse width 1 microsec. A row of "1"s and a row of "0"s are
represented respectively by two different d.c. levels. This
type of pulse is normally used in arithmetic units, where
successive digits of two input signals are combined to generate
the pulses of a waveform representing, say, the sum of the
numbers coming in. This technique eliminates most of the effect
of the timing errors inevitable at these speeds of operation.
For instance, a timing difference of 0.2 microsec between the
two input waveforms would remove two-thirds of the overlap bet-
ween two narrow pulses, while the period of coincidence between
two wide pulses would be cut by only 20%. Wide pulses are also
used in the DELAY elements of the storage, in this case modu-
lating a carrier signal of frequency 16 Mc/s.
The three possible signals representing the number "13" are shown in
Figure 3.1. In the first two cases, either positive or negative pulses
may be used. Since the types of signal are used for different purposes,
it is often necessary to generate signal (b) from signal (a) and vice
versa.
LOGICAL DIAGRAMS AND SYMBOLS
In describing the operation of parts of the DEUCE, three main types
NS-y-37/11-57
of diagrams will be used. Two of these, the circuit diagram and the
conventional "block schematic", need no explanation. The third type,
which is peculiar to this kind of work, is the Logical Diagram. This
also consists of a number of symbols connected together by lines which
carry signals. The nature of these signals, however, is not specified;
they are either present or absent, and have no other characteristic.
Each symbol represents a logical unit which gives an output signal
completely determined by its one or more input signals. The electronic
circuit by which this required effect is achieved may take any of a
number of forms, but the same logical symbol is used for all. Each line
is marked with an arrow, and can convey a signal in only one direction.
The polarity of a signal has no place in a logical diagram, nor have
such units as power amplifiers. It is even possible to give a complete
logical diagram of the DEUCE without referring to wide and narrow pulses.
This will not be attempted here, since the present object is to explain
the operation of the Machine in terms of its circuits, using logical
diagrams only as an immediate stage. A logical diagram may be regarded
as dealing directly with numbers, a signal which is present in alternate
microsecs, for instance, being written "010101 ...".
LOGICAL SYMBOLS
The logical symbols which will be used in this report are set out in
Figure 3.2 and described below. Typical input anal output signals are
given in each case:
One-Gate
A signal appears at the output whenever a signal is applied to either
(or both) of the two inputs. In cases where simultaneous signals at the
two inputs cannot occur, the One-Gate may be replaced by a simple
connection.
Inhibitor-Gate
The signal at the normal input (A) appears unchanged at the output,
provided there is no signal at the inhibitor input (B). With a signal at
the inhibitor input, there is no output, whatever the normal input.
Two-Gate
A signal appears at the output only when one is applied to both of
the two inputs. In practice, at least one of the two inputs to any gate
must have wide pulses, to avoid timing difficulties.
General Gate
This has any number of normal and inhibiting inputs and is marked
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with the number "n". Output signal occurs Only if "n" or more of the
normal inputs carry signal, and none of the inhibiting inputs do.
Negator
A negator has one input and one output Connection. It gives a signal
at the output if, add only if, no signal is applied to the input.
Unit Delay
The input is exactly reproduced at the output, except that each
digit appears 1 microsec later. Longer or shorter delays are indicated
by writing the delay, in microsecs, inside or beside the "D".
Beginning Element
This gives a single pulse at the output starting coincidentally with
the beginning of any continuous signal at the input.
End Element
This gives a single pulse at the output starting coincidentally with
the end of any continuous signal at the input. For a particular begin-
ning or end element, the duration of the "single pulse" at the output is
fixed by the values of the electronic components. There are a large
number of such elements in the Computer, with output pulses varying from
a small fraction of a microsec to several millisec, depending on the
function which the output signal is required to perform. The exact
width of the output pulse is never critical; its approximate duration
will in general be clear from the context.
Trigger
A signal at the trigger input (J) is said to "stimulate" the trigger
or to put it on. One at the inhibitor input (K) "clears" the trigger, or
puts it off. So long as the trigger is on it gives a continuous signal
at the output which represents a succession of "1"s. A signal at the
trigger input while it is on, or one at the inhibitor when it is off, has
no further effect. The output is always in the form of wide pulses. The
inputs may be either wide or narrow pulses, or, in fact, any other form of
signal pattern.
Changeover Trigger
This trigger is stimulated and cleared by alternate signals at the
same input. A signal arriving while the trigger is off puts it on, and
vice versa.
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Widener
A narrow pulse of signal at the input initiates a 1 microsec pulse
of signal at the output, beginning the same time as the input signal. It
will be seen from the figure that the centre of the widened pulse is
nearly half a microsec later than the centre of the original narrow
pulse; thus a widener always introduces a concomitant delay of about
half a microsec.
Longer Delays
Delays of 32 microsec or more used in the high-speed store will be
denoted by a box with the delay period written inside.
Composite Gate
This has two outputs, one giving signal only when the two inputs
differ, and the other giving a signal only when there is signal at both
inputs. The diagram shows how these functions could be built up, as they
usually are, by combination of previous symbols. The special symbol has
been introduced here to give closer correspondence with the electronic
circuit.
Input Signals
The operation of the computer may be modified by an external stimu-
lous from the Main Control Panel or elsewhere. A source of such stimuli
is represented by a square box with one output connection which carries
signal when the source is stimulated and not otherwise.
Examples of Logical Diagrams
Figure 3.3 shows two small examples of the use of these symbols in
combination.
Multiway Gate
To connect a selected one of five input signals on to a common out-
put line, a control signal is sent to the appropriate 2-Gate and to none
of the others. So long as this signal is maintained, this Gate gives an
output which is the same as its input; the others give no output at all.
A similar circuit will connect a common input signal to a selected one of
several output lines.
Changeover Gate
A single control signal is used to choose between only two alterna-
tive connections. With no control signal, input 1 passes through Gate A
to the output and gate B gives no signal. When a continuous central
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signal in applied, Gate A is inhibited and gate B gives a signal which
reproduces input 2.
Source and Destination Gates
Figure 3.4 shows a few bits of the Machine drawn in the new notation.
The "Highway Amplifier" box at the top is a power Amplifier which intro-
duces a short delay (about 0.15 microsec); for this reason, the sections
of Highway connected respectively to the Sources and to the Destinations
are called "Highway (Early)" and "Highway (Late)" Pulses on Highway
are always narrow; each delay line therefore has on associated widener,
modulator, detector and clock-pulse gate; these are not shown in the
diagram. Signal is always supplied to just one of the lines S0, S1 ...
S31, and one of the lines DO, D1 ... D31 and one of the lines N0, N1 ...
N7. The Destination selector signal is effective only in conjunction
with Transtim.
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FUNDAMENTAL WAVEFORMS
The operation of the DEUCE is controlled by certain basic waveforms
Which determine the timing of the digits and, where necessary, distinguish
Between the digits of a word.
CLOCK PULSES
This signal is a continuous sequence of pulses, 0.3 microsec wide,
at 1 microsec intervals. It is used in converting a word from wide to
narrow pulses, and thus controls the timing of digits throughout the
Machine. A "Clock-Pulse Gate" is shown in Figure 4.1.
Q-PULSES
There are 32 of these signals, corresponding with the successive
digits of a word. They are known as "Q1", "Q2", and so on, up to "Q32".
Each consists of a 1 microsec pulse repeated every 32 microsec; it
would represent, in wide pulses, a number with 31 zero digits and a "1".
In Q1, this single pulse coincides with the first digit of a word; in
Q2, with the second, and so on. The signals are shown in Figure 4.2;
they are used to initiate any action required at a particular time in the
minor cycle and to pick out a particular digit from a word. This second
function is important in interpreting instructions and in the input and
output mechanisms.
The narrow equivalent of a Q-pulse is a "P-pulse". Only a few of
these are used, and they are generated from the corresponding Q-pulse by
a Clock-Pulse gate in the particular chassis where they are wanted.
THE INPUT DYNAMICISER
The number is first presented to the Machine in parallel form, that
is with all the digits there at once, spread out across a row of relays
or of holes punched in a card. Before it can reach the storage or the
arithmetic units, the number must be translated into serial form, with
all the digits appearing on a common line, one after another. This is
done in a set of 32 circuits known collectively as the "Input
Dynamiciser".
The first six stages of the I.D. are shown in Figure 4.3. The
switches which are "on" represent energised relays or holes punched in
one row of a Hollerith card. The others are unenergised relays or blank
spaces on the card. They are set in the diagram to represent the number
13. In successive microsecs Q1 flows through its switch to the common
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line, Q2 appears, but gets nowhere, Q3 and Q4 go through and Q5 and Q6 are
baulked. The final signal is shown before and after "clocking".
THE OUTPUT STATICISER
The reverse translation from serial to parallel form is needed before
a number can be displayed on a row of lamps or punched on a row of a card.
This is done by the Output Staticiser, six stages of which are shown in
Figure 4.4. The input signal is again the number 13, expressed in narrow
pulses. Suppose that initially, all the triggers are off. In the first
microsec, a narrow pulse arrives at the input and is presented at all the
2-Gates; at this time, only the Q1 line carried a signal, so only this
gate gives an output, which stimulates the first trigger. In the second
microsec, no pulse appears at the input, and nothing happens. Two succes-
sive pulses now arrive, the first combining with Q3 to give an output
which stimulates the 3rd trigger, and the second coinciding with Q4 to
put the fourth trigger on. No further pulses arrive at the input, and
none of the remaining triggers in struck. The number 13 is now
represented in parallel form by signals coming from only the 1st 3rd and
4th of the row of 32 triggers. These triggers are connected either to
the 0.S. lamp on the Control Panel or to the magnets in the Hollerith
Punch which control the punching.
Before a second word can be set up on the O.S., all the triggers
must be cleared by a signal on the "Clear O.S." line. When using the
row of lamps, this signal may be supplied either by obeying the Instruc-
tion "18-24" which uses Destination Triggers, or by pressing a key on the
Control Panel. When punching numbers on a card, the signal is auto-
matically supplied by the Hollerith Punch as soon as each row has been
punched.
To staticise or dynamicise a word takes a time of 32 microsec. This
causes no difficulty, since a row of a card remains under the read
brushes or punch knives for much longer than this. So far, we have
considered input and output only in binary form; no extra provision is
made for decimal input and output, since a card is read or punched one
row at a time as a sequence of twelve binary configurations, even if the
pattern of holes in it is intended to represent one decimal number. The
problem of combining these twelve configurations to form the same number
in binary form, or of creating them from a single binary number, is one
of programming rather than Machine design.
THE OSCILLATOR
The fundamental timing waveform is generated by an oscillator
circuit, controlled by a crystal to a frequency of exactly 1 Mc/s. This
signal ultimately controls the timing of individual digits throughout
the DEUCE. Three connections are taken from the oscillator, as shown in
Figure 4.5.
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From the lowest of the three output connections shown, the original
1 Mc/s signal is taken to the Divider where it controls, eventually, the
timing of the Q-Pulses.
The Clock-pulses are generated directly from the 1 Mc/s signal in a
Shaper circuit, and transmitted through a power amplifier to the middle
Output connection. The amplifier is needed because of the large number
of points in the Machine to which this terminal is connected, and the
correspondingly large output capacity. Between the oscillator and the
divider is a phase-shifter circuit incorporating a manual control;
varying this adjusts the timing of the Q-Pulse signals relative to the
Clock-pulses (Figure 4.6).
The signal at the upper output connection is an 8 Mc/s sine wave;
this is connected to every storage position, in each of which the
frequency is again doubled to give the 16 Mc/s signal which provides the
carrier wave in the mercury delay lines.
THE DIVIDER
The main object of the Divider is to generate from the original 1
Mc/s waveform an output waveform with a period of 32 microsec. This is
subsequently used to drive, in succession, the 32 circuits generating
the Q-Pulse waveforms. There are also two outputs which control the
precise timing of the Q-pulses.
The logical arrangement of the divider is shown in Figure 4.7. It
Consists mainly of a chain of five changeover triggers connected together
with beginning elements. The first is operated by the 1 Mc/s waveform;
it is therefore on and off for alternate periods of 1 microsec, giving
a waveform at B whose total period is 2 microsec. A narrow pulse is
therefore applied to the second trigger every 2 microsec; this trigger
is thus on and off for alternate periods of 2 microsec, giving a narrow
pulse every 4 microsec at F. This process continues until, finally, a
narrow pulse occurs at L once every 32 microsec, coincident with one of
the pulses at D which drive the Divider from the second stage onward.
The pulses at K1 and K2, each with a period of 2 microsec, are
Exactly interleaved. The K1 signal controls the end of every odd
Q-pulse, that at K2 the end of every even Q-Pulse. Trigger "DRS" is
stimulated every 32 microsec by the pulse at L, and cleared by the next
K1 pulse, 1 microsec later. Its output signal, however, lasts for
slightly less than 1 microsec, since the pulse at L is in practice later
than the corresponding K2 Pulse, owing to the circuit delay in the last
four divider stages. The final output at N, or "R(out)" is thus a pulse
occurring every 32 microsec, truly coincident in time with one of the K1
pulses. This pulse is used to initiate the Q32 pulse. The vertical lines
at the bottom of the waveform chart indicate the end of successive minor
cycles.
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RING STAGES
The Q-pulses are generated by 32 identical circuits, called "Ring
Stages". Figure 4.8 shows the connections between the R(out) signal from
the Divider and the first five ring stages. Each ring stage comprises
a trigger and an End element. The trigger is stimulated by the clearing
of the previous trigger, and cleared alternatively by a pulse from K2
and K1. The operation is clear from the waveform chart. The other 27
ring stages follow in just the same way; the last trigger is cleared
just as the next pulse arrives at R(out) from the Divider to restimu-
late the first. No use is made of the narrow output pulse from the last
End element, which is left unconnected.
The narrow pulses marking the microsecs are separated on to the two
lines K1 and K2 because if they were all presented on one common line,
the stimulating and clearing pulses to each trigger would arrive
simultaneously.
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THE CIRCULATION UNIT
The first part of the machine to be described in detail will be the
Circulation Unit, one of which is associated with each delay line storage
position. There are 22 of them, all identical; special facilities such
as the addition and subtraction into TS13 are attached by connecting an
appropriate special unit to certain connection points which are provided
on all circulation units but not always used. The layout of a storage
position is shown in block form by Figure 5.1. It will be explained by
tracing the passage of a signal round the loop, starting at the point "H".
The Signal at H, consisting of narrow pulses, enters the Widener, a
standard circuit from which the digits emerge as wide pulses. These go
to the Modulator, where they modulate a 16 Mc/s carrier wave, generated
by the Frequency Doubler from the common 8 Mc/s signal which enters the
circulation chassis from a screened cable.
The signal leaves the Circulation Unit in this form through a
screened cable which takes it to the Transmitter; this is contained in
a small box mounted near to the mercury column. In effect, it generates
a powerful copy of its input signal, which it sends along a further
screened cable to a Piezo-Electric Crystal which is in intimate contact
with the mercury. The function of this crystal is to vibrate in sympathy
with the applied electrical signal, and so to transmit sound waves of the
same frequency, which travel through the Mercury Delay Line.
At the far end of the delay, the pulses of sound hit a second Piezo-
Electric Crystal, which has the reverse function of accepting the acoustic
waves and giving out electrical signals of the same frequency. These pass
through a Transformer which matches the impedances of crystal and cable
(there is one at the input end. too), and through a screened cable to the
Receiver. This is mounted near to the delay, and it revives the pulses,
by this stage rather weak, before sending them through another screened
cable back to the Circulation Unit.
The signal new passes through the Detector, which removes the 16 Mc/s
element and emerges as wide d.c. pulses. A conventional Clock-Pulse Gate
is used to generate two narrow-pulse signals; that at "J" represents the
words being stored, while the digits at "N" are the negated version.
In most cases, J is connected to K, and N is not used. In certain
Storage positions, however, the signal is taken from J (and also from N,
in some form of them) to a special unit of some kind; such a unit must
have, among others, one output terminal where the signal J emerges
unchanged in form, so that it can be connected back to K and so complete
NS-y-37/11-57
the circulation path. An example is the Logical Operations unit, which
takes signal from both J14 and N14 and returns a signal to K14. (The
Logical Operations unit also takes signal from J15 and N15, but without
breaking the circulation path of TS15).
From K the narrow pulses pass to the Source Gate, which is connected
to Highway (Early), to one of the outputs of the Source Selector Tree and
to a point called SC which will be explained later. Before entering the
Destination Gate, to which is connected the TT signal, an output from the
Destination Selector Tree, and HWL, the signal passes through a Delay
Network, which introduces a delay of 0.15 microsec. The precise object
of this delay, which compensates for the delay in the Highway amplifier,
will be discussed below. The Source and Destination connections are a
little more complicated than so far explained (see section on "Selector
Trees").
Next comes the NIS gate; in the first eight Delay lines, this is
connected to the NISC line, IHW and the NIS Tree. The signal emerges at
G Normally, G is connected directly to H; in some cases, however, the
signal at G passes through a special unit. From which it emerges in the
same form to be returned to H. An example is TS13, in which is inserted
the Adder Unit. This completes the circulation path; the words in store
circulate indefinitely, until replaced by a new input at the Destination
gate. They may, however, be modified by the special units inserted at
J-K or G-H.
REGENERATION
The passage through the mercury and the processes of modulation and
Detection introduce a degree of distortion in the signal. Also, although
the length of each mercury column is adjustable, there is bound to be
some error of timing. However, so long as the pulse reaching the Clock-
Pulse gate is large enough to be recognisable, and so long as it is not so
wide, narrow, late or early that one or both of its edges reaches the Clock
Pulse on either flank, the output from the Clock-Pulse gate is just as
sound in shape and timing as that which would be generated by a perfect
input pulse.
The errors of shape and timing are thus not cumulative; if a pulse
will make one lap of the circuit without harm, then (with reasonable
margins of safety) it will circulate unharmed indefinitely,
TIMING
The Widener, as has been pointed out, effectively introduces a delay
of about 0.35 microsec; this, as well as the delay network between K and
G, must be compensated by shortening the mercury line to give a delay about
0.6 microsec less than its official value.
NS-y-37/11-57
In some cases, a special unit inserted at J-K or G-H introduces a
delay of 1 microsec; these delays must also be compensated by a corres-
ponding shortening of the mercury line.
A pulse at K occurs at the same time as the corresponding digit on
HWE but about 0.15 microsec before that HWL. The effect of the delay
network is that a pulse has the same timing at H whether it came
straight through from K or had just entered at the Destination gate. In
consequence, all pulses arrive at the Clock-Pulse gate with the same
timing, giving a greater margin of error than would be obtained if a
range of different input timing had to be safely accommodated.
INDIVIDUALITIES
The 22 Circulation Chassis are identical, and each contains the
same equipment, including the Source, Destination and NIS gates. Not
all of these, however, are connected in the standard manner described
above. In the 21 storage positions, the Source and Destination gates
are all normal, as are the NIS gates of the first eight Delay Lines.
The other NIS gates are not used, the NISC, IHW and NIS Tree terminals
being left unconnected.
In TS COUNT, none of the three gates is normally connected. They
are all used for special purposes which will be described in the chapter
on Control.
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CONTROL
THE INSTRUCTION WORD
The Instruction word comprises seven separate numbers of up to five
digits each.
Digits Name, Possible Values and Function
2 to 4 NIS (0 to 7) Number of Selected NIS gate.
5 to 9 S (0 to 31) Number of selected Source gate.
10 to 14 D (0 to 31) Number of selected Destination gate.
15 & 16 C (0 to 3) Characteristic. Determines the length of
Transfer as explained below.
17 to 21 W (0 to 31) Wait number. Number of idle minor cycles
between Set-up and 1st m.c. of Transtim.
26 to 30 T (0 to 31) Timing number. Specifies the m.c. of the
next instruction and sometimes the last
m.c. of Transtim.
32 G (0 or 1) Go digit. Function explained in conjunc-
tion with details of Control.
Digits 1, 22 to 25 and 31 are spare; they are ignored by Control and
their value has no effect on the operation.
CHARACTERISTIC NUMBER
The function of the Timing number is modified by the value of the
Characteristic, which effectively divides Instructions into three types,
each of which is given a special name:
Single Transfer -
C is 0. Transfer is for 1 m.c. only.
Long Transfer -
C is 1. The number of m.c. for which TT is applied is determined by
the values of W and T.
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Double Transfer -
C is 2. Transfer is for just two minor cycles.
(The Characteristic is not normally given the value 3).
The details of timing will first be described for a Long Transfer.
TIMING OF TT AND TCI SIGNALS FOR A LONG TRANSFER
Figure 6.1 gives an example of the timing of TT and TCI in a Long
Transfer (C = 1) in which W is taken as 2 and T as 4. The Instruction in
question is stored in m.c. 7 of some DL; it appears on IHW in this m.c.,
and is let into TS COUNT by the application of TCI Signal. In m.c. 8
the Instruction first enters the main part of Control from the delay
element of TS COUNT, and the various gates are selected in accordance
with the NIS, S and D numbers. Minor cycle 8 is thus the Set-up m.c.
After Set-up, there is a pause of W m.c.; in the figure, W is 2,
and the pause occupies minor cycles 9 and 10. If the Wait number were 0,
Transtim would first have been applied in m.c. 9; as it is. Transfer
commences in m.c.11.
The Timing number has a dual function, affecting both TT and TCI.
The last minor cycle of Transfer, which is also the single m.c. for which
TCI is applied, is the T + 1th after Set-up and the T + 2th after that in
which the Instruction was stored. In the example, this is the 5th m.c.
after Set-up, or m.c.13. The transfer occupies minor cycles 11, 12 and 13.
The next Instruction enters TS COUNT in m.c.13. It must therefore
have been stored in m.c.13 of the Delay Line referred to in the NIS
number. It enters TS COUNT while the Transfer specified by the previous
Instruction is still in progress, but it does not affect the operation
until the following minor cycle, in which it first enters the main part
of Control. Its NIS, S and D numbers are set up in m. c.14.
GENERAL CASE
The minor cycles of operation are usually referred to the minor cycle
in which the current Instruction is stored, and in which (by definition)
it enters TS COUNT. We will call this minor cycle "m".
The Set-up minor cycle is m.c. m + 1.
Transfer commences in m.c. m+w+2.
The next Instruction is stored in m.c. m+T+2.
(These three numbers hold for any value of Characteristic).
The last m.c. of Transfer Is m+T+2, so that the number of minor cycles
of Transfer is T-W+1.
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W GREATER THAN T
The last minor cycle of Transfer clearly cannot precede the first.
If W exceeds T, the effective value of T is increased by 32. Minor cycle
m+T+2 is ignored, Transfer starts In m.c. m+W+2; the minor cycle in which
Transfer ends and the next Instruction enters TS COUNT is m.c. m+T+34,
or m+T+2 of the next Major Cycle. The next Instruction is still stored
in m.c. m+T+2, but only at its second appearance on IHW is the TCI gate
opened to let it into TS COUNT.
As an example, take an Instruction stored in m.c.27 whose Wait and
Timing numbers are 10 and 1 respectively. The minor cycles of Transfer
are from 39 to 62, that is from 7 to 30 of the next Major Cycle. The
next Instruction is stored in m.c.30, and enters TS COUNT at its second
attempt.
SINGLE AND DOUBLE TRANSFERS
The minor cycles in which Transtim commences and in which TCI is
applied are the same for all values of C, being m+W+2 and m+T+2
(or m+T+34) respectively. The Characteristic affects only the end of
Transtim. If C is 0, Transtim is applied for only one minor cycle,
m+W+2; if C is 2 Transtim is applied for two minor cycles, m+W+2 and
m+W+3. The effect of Single and Double Transfer Instructions is shown in
the diagram by dotted lines.
When W = T and C = 2 the next Instruction cannot enter TS COUNT in
m.c. m+T+2, since this would precede the second minor cycle of transfer
m.c. m+W+3, specified by the Characteristic. Instead, in this special
case, its next Instruction enters TS COUNT in m.c. m+T+34.
DETAILED OPERATION OF CONTROL
For simplicity, the logical diagram of Control will be given in
sections, illustrating only that part currently under discussion. Figure
6.2 shows two features, the detailed input mechanism and the Unit
Subtractor, represented as a block.
DESTINATION 0
Normally, the word entering TS COUNT comes from IHW, which is con-
nected only to the first eight Delay Lines. It is possible, however, by
using Destination 0, to inject into TS COUNT any word which is available
at a Source. If D0 is selected, and TT is applied in the same minor
cycle as TCI, the word entering TS COUNT will be the one appearing in that
minor cycle, not on IHW, but on HWL.
Suppose, as an example, that the word currently in TS16 represents
the Instruction which is to be obeyed next. A preliminary Instruction is
necessary which might be:
NS-y-37/11-57
N S D C W T
X 16 0 1 0 5
This preliminary Instruction reaches TS COUNT in. say m.c.9 in the usual
way, through IHW, having been stored in m.c.9 of one of the first eight
DLs. S16 and DO are set-up in m.c.10, and TT is applied from m.c.11 to
m.c.16. During this time, the word in TS16 is repeatedly applied to the
TCI input gate to TS COUNT. From m.c.11 to m.c.15, this gate is shut,
but finally, in m.c.16, TCI is applied and the word from TS16 enters TS
COUNT. The Wait and Timing sections of the word in TS COUNT must be
calculated as if the word had been stored in m.c.16 of one of the first
eight Delay Lines. The NIS number of the preliminary Instruction is
immaterial, since it affects only the words on IHW, none of which
succeeds in reaching TS COUNT.
This procedure uses two Instructions, the preliminary one and the one
in TS16, to obtain one useful Transfer, that specified by the Instruction
in TS16. The facility is very useful, however, for the initial input of
Instructions from the Hollerith Reader and for using Instructions which
have been modified in some way by the arithmetic units. The TCI gate, by
the way, is the normal Destination Gate in the TS COUNT circulation unit.
THE UNIT SUBTRACTOR (FUNCTION)
The Unit Subtractor takes in the Instruction word at "A" and sends
it out again at "B", unchanged except that 1 has been subtracted from
each of the Wait and Timing numbers. If the word at "A" is "N,S,D,C,W,
T,G", it will emerge from "B" as "N,S,D,C,W-1,T-1,G". The values of T
and W are thus decreased by 1 for each circulation through TS COUNT.
The Unit Subtractor also gives signals at "C" and "D", which indicate
when the Wait and Timing numbers, respectively, have been reduced to
zero. "C", which gives a signal W m.c. after the Instruction entered
TS COUNT, initiates the start of TT, and "D" initiates the end of TT (if
the Characteristic is 1 in the Instruction) and the m.c. of TCI.
Finally, the Unit Subtractor gives a signal at "E" which consists
of the Instruction word negated. This goes to the circuits which select
the appropriate NIS, S and D.
UNIT SUBTRACTOR (OPERATION)
Two examples will first be given of the subtraction of "1" from a
binary number (least significant digit on the left).
1 2 4 8 16 1 2 4 8 16
0 0 1 1 1 (28) 0 1 0 0 0 (2)
1 1 0 1 1 (27) 1 0 0 0 0 (1)
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In each case, the lower number could have been obtained from the
upper by negating all digits up to and including the first "1" and
leaving the others unchanged. This procedure, in fact, always has the
effect of subtracting "1" from the number to which it is applied, and
forms the basis of the operation of the unit Subtractor.
The details of the Unit Subtractor are shown in Figure 6.3. The
connection marked "from Trigger S" is associated with the double transfer
operation and may be ignored for the moment. The Instruction word
emerges from the TS COUNT delay element in wide-pulse form; the points
"J" and "N" both carry narrow-pulse words, at "J" the Instruction word
and at "N" the same word negated. This clock-pulse gate is the normal one
in the TS COUNT circulation unit. The signal emerging at "B" will be the
"J" signal if Trigger CARRY is off and the "N" signal if it is on. The
word "J" is thus returned unchanged to "K", except that those digits which
occur while Trigger CARRY is on are negated.
Trigger CARRY is stimulated by very narrow pulses of signal which
mark the back edges of Q16 and Q25. It is cleared at the end of any
microsec in which a digit "1" appears at "J". Figure 6.4 shows the
outputs from CARRY and at "B" in response to an input word at "A" whose
Wait and Timing numbers are 28 and 2 respectively; 1 has been subtracted
from both W and T. The output from CARRY includes neither Q22 nor Q31,
so there is no output from "C" or "D".
"C" gives an output only if the signal from CARRY extends to cover
Q22, which means that all the five Wait number digits at "A" must be zero.
This occurs in m.c. m+W+1, where the original Instruction entered TS COUNT
in m.c. "m" and had Wait number "W". The subtraction process continues,
and the W section of the word at "A" is again zero after a further 32 unit
subtractions, giving a second pulse of signal at "C". The output at "C"
is thus P22 in m.c. m+W+1, and in m.c. m+W+1 of every subsequent Major
Cycle until the word in TS COUNT is replaced by the next Instruction.
Very often, the Instruction is replaced before the second signal is due at
"C" which then gives only one pulse for each Instruction.
Similarly, the output at "D" is P31 in m.c. m+T+1, of every Major
Cycle until the Instruction is replaced. Figure 6.5 shows the operation
for zero Wait and Timing numbers at "A", though these, in practice, occur
in the same minor cycle only if the original W and T were equal. The
Timing number at "J" now provides no signal to clear Trigger CARRY, which
is therefore extinguished by the front edge of a Q32, to prevent its
remaining on and negating Go digit and possibly part of the NIS number.
Trouble would also arise from a pulse at P16 or P25 time at "J",
which would try to clear Trigger CARRY just at the moment when other
pulses were arriving to stimulate it. This is avoided by removing any
such digits by an inhibitor gate.
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THE INSTRUCTION STATICISER
The signal from "E" is used to select the required NIS, S and D
gates. It is first taken to a set of 14 circuits called the "Instruction
Staticiser". The output at "E" is therefore usually called the "IS"
signal. The Instruction Staticiser, shown In Figure 6.6, may be des-
cribed as a negated version of part of the Output Staticiser. Its output
is a parallel version of 14 digits of the word in TS COUNT.
In the Output Staticiser, the "Clear OS" signal puts all the OS
triggers off, and individual ones are put on by pulses at the appropriate
time in the OS input word. In the Instruction Staticiser, on the other
hand, the "Clear IS" signal puts all the IS triggers on, and individual
ones are put off by pulses at the appropriate time in the IS input word
from "E".
The "Clear IS" signal is a short pulse at the end of the TCI signal;
it therefore occurs just as a new Instruction has finished entering TS
COUNT but before it emerges in negated form at "E". Suppose, for example,
that this new Instruction has NIS number "6", meaning that its 2nd, 3rd
and 4th digits are 0, 1, 1 respectively; the corresponding digits at "E"
are 1, 0, 0. The IS signal has a pulse in Q2 time, which clears Trigger
IS2, but not during Q3 or Q4; triggers IS3 and IS4 thus remain on. The
next 11 digits, up to the 15th, are staticised in the same way; this
process takes place during the set-up minor cycle, at the end of which,
the IS trigger outputs give the static equivalent of the "Address" section
(digits 2 to 15) of the word in TS COUNT.
The (negated) word in TS COUNT appears repeatedly on IS, but the IS
triggers are unaffected after the first time; the subtracting process
does not affect the Address section so that the pulses are merely applied
to the "Clear" input of triggers which are already off. The pulses are
inhibited while TCI signal is applied to let the next Instruction into
TS COUNT; the reason for this will become clear when we consider the
discrimination facilities.
THE EXTERNAL TREE
The outputs of the first 14 IS triggers (IS2 to IS15) may be replaced
with signals from 13 "IS Keys" and a "Characteristic Key" on the Control
Panel. This is done by pressing another key on the Control Panel called
"External Tree".
SELECTOR TREES (FUNCTION)
13 of the IS trigger outputs are taken in groups to three "Selector
Trees" represented in Figure 6.7 by blocks. The IS2, IS3 and IS4 signals,
for instance, go to the NIS Selection Tree; this then gives an output on
one of eight possible output lines. Which of the output lines is chosen
NS-y-37/11-57
at any given time is determined by the particular one of the eight pos-
sible binary configurations then being applied at the three IS input
lines.
The Source and Destination Selector Trees are also shown as blocks,
each having five IS input lines and 32 possible output lines. Their
operation is more complicated than that of the NIS Tree, and some
further explanation will be given at the end of the description of
Control.
The output of trigger IS15, representing the first digit of the
Characteristic number, is taken, not to a Selection Tree, but to the
Section of Control governing the operation of Transtim.
TRIGGER R AND Q
The N, S and D numbers of the Instruction word determine the IS
trigger settings, which in turn control the three Selector Trees. The
Wait and Timing numbers determine the minor cycles in which signals occur
at "C" and "D"; these signals, in turn. control the operation of TT and
TCI.
In the first place, the signals at "C" and "D" operate two triggers,
Trigger R and Trigger Q, as shown in Figure 6.8. Trigger GO, also shown
in the diagram, will be assumed to be permanently on; its operation will
be ignored for the moment. The output of the two triggers is shown in
Figure 6.9 which also gives, for comparison, the required TT and TCI
signals. Trigger GO being on, Trigger R is stimulated by the first pulse
of signal at "C", which occurs at P22 of m.c. m+W+1; Trigger Q is stimu-
lated by the first pulse of signal from "D" after Trigger R has been put
on. If T is less than W, the first signal at "D" has no effect, and
Trigger Q comes on at P31 in m.c. m+T+33; otherwise, at P31 in m.c.
m+T+1. If T and W are equal, the two triggers are stimulated at P22 and
P31 in the same minor cycle (except, as we shall see, in the case of a
double transfer).
Trigger Q stays on for less than one minor cycle, being stimulated
at P31 and cleared at the beginning of the next Q22 signal. Trigger R
is also cleared at this time, by a short pulse occuring at the end of the
signal from Trigger Q. The output of Trigger R governs the generation of
the Transtim signal; it is also used in the Discrimination facilities,
which have yet to be described. The output of Trigger Q governs the
generation of TCI.
TRIGGERS S, P AND TT
Figure 6.10 shows the part of Control which generates the Transtim
signal. The signals from the various triggers are given in Figure 6.11.
There are three possible modes of operation. depending on whether the
Transfer is to be Long, Single or Double.
NS-y-37/11-57
In all three cases, Trigger P comes on at the same time as Trigger R.
In a Long Transfer there is a signal from Trigger IS15, and Trigger P
remains on until it is cleared by a short pulse at the end of the signal
from Trigger R. The outputs of Triggers R and P are thus identical.
Trigger TT is controlled by short pulses of signal at P32 time; its
output is passed through a delay network of 0.5 microsec, so that the
final output exactly spans one or more minor cycles. The point of this
arrangement is that the 0.5 microsec delay can be shortened to compensate
for any stray delays in the subsequent circuits. TT is stimulated by the
first of these P32 signals after Trigger P comes on and cleared by the
first one after Trigger P goes off. In the case of a Long Transfer,
Trigger TT comes on at the end of m.c. m+W+1 and goes off at the end of
m.c. m+T+2.
In both Single and Double Transfer Instructions, the Characteristic
is even, the 15th digit is "0" and IS15 is cleared by the IS signal and
remains off throughout the operation. As we shall see, this means that a
Q14 signal is released from gate "F" to clear Trigger P in either the
first or second minor cycle after it is stimulated.
The distinction between Single and Double Transfer Instructions is
determined by Trigger S. This has the function of staticising the 16th
digit of the Instruct on, but it differs in two respects from a normal
IS trigger. Firstly, it is cleared by CIS and stimulated by a P16 pulse
from "J" instead of being stimulated by CIS and cleared by a P16 pulse
from "N"; secondly, instead of remaining on until the next Instruction
enters TS COUNT, it is cleared in the coarse of interpreting and obeying
the current Instruction. A point to note is that any P16 digit at "J"
is inhibited in the Unit Subtractor at its first appearance, and makes no
further attempt to stimulate Trigger S; once this is cleared, it there-
fore is not restimulated until the arrival in TS COUNT of another Double
Transfer Instruction.
The detailed operation of the three types of Instruction will now be
described.
LONG: m.c. m+W+1 :- P comes on with R at P22;
TT comes on at P32.
m.c. m+T+1 :- Q comes on at P31.
m.c. m+T+2 :- P goes off with Q and R at Q22;
TT goes off at P32.
SINGLE: m.c. m+W+1 :- P comes on with R at P22;
TT comes on at P32.
m.c. m+W+2 :- P goes off at Q14;
TT goes off at P32.
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DOUBLE: m.c. m+W+1 :- as before.
m.c. m+W+2 :- Q14 from gate "F" is inhibited by Trigger S;
S goes off at Q19.
m.c. m+W+3 :- P goes off at Q14;
TT goes off at P32.
It will be seen that Trigger S is always cleared before the CIS signal
arrives at the end of m. c. m+T+2, the minor cycle of TCI. The CIS connec-
tion is, in fact, necessitated only by the operation of the Discrimination
facilities. A connection is taken from Trigger S to inhibit the signal
from D which stimulates Trigger Q. If Trigger S is on, this prevents
Triggers R and Q coming on in the same minor cycle, as required for a
double transfer with equal Wait and Timing numbers.
CONTINUOUS TRANSTIM
Pressing a key on the Control Panel labelled "Cont T.T." injects a
signal connected to the output of Trigger P. This causes TRANSTIM to
come on at the next P32 and to stay on. The result is continuous transfer
between the selected Source and Destination.
PbD6
It is required for various purposes around the Machine to have a short
signal which occurs a little before the beginning of Transtim. This is
provided by taking a connection from Trigger P through a beginning element
and a delay of 6 microsec (see Figure 6.10). The result is a brief pulse
of signal at about P28 time in the minor cycle immediately preceding the
first minor cycle of Transtim; this is known as "Trigger P (beginning)
delayed 6 microsec", or PbD6 for short. It is used in Destination Triggers
and a device called "Control-Magnetic Interlock" (CMI) which will be des-
cribed in the next paragraph.
CONTROL-MAGNETICS INTERLOCK
In the chapter on the Magnetic Store, it will be found that any
operation involving the Magnetics occupies at least 13 millisec. To save
time, it is arranged that each such operation is initiated by an Instruc-
tion obeyed in Control and then proceeds to completion under its own
steam, leaving the rest of the DEUCE free to do any other sequence of
operations required by the computation in hand.
However, this method has the snag that while this first Magnetic
operation is still in progress the program may proceed as far as a
second Instruction intended to initiate a Magnetic operation, with the
result that the Magnetics would be required to do two things at once,
which it cannot. To avoid this trouble, the second Instruction is held
NS-y-37/11-57
suspended in TS COUNT until the completion of the first Magnetic operation,
and the Program proceeds no further until this time.
Let us state the requirements ware precisely:
whenever (a) a Magnetic operation is in progress
and (b) the Instruction about to be obeyed would initiate a further
Magnetic operation
then this Instruction is not obeyed but is held over until the
completion of (a).
The information (b) that a Magnetic operation is about to be called
is taken into the Magnetics organisation by connections from the IS
Triggers; here, it is combined with the information (a) that a Magnetic
operation is already in progress to generate a warning signal which is
taken to Control on a line called "Control-Magnetics Interlock" or CMI.
The circumstances and circuits in which CMI signal is generated will
be described in the chapter on Magnetics; these circumstances will be
seen to be a little more complicated than has yet been indicated. Here
we are concerned only in the action of CMI signal in suspending the
operation of Control.
The connections are shown in Figure 6.12. It will be remembered that
PbD6 signal occurs at about Q28 time in m.c. m+W+1; if CMI signal is
present, this PbD6 signal (gated with Q28 to fix the timing precisely) is
used to clear Trigger R. Trigger P is in turn cleared by the end element
connecting it with Trigger R; furthermore, Trigger Q never comes on,
since Trigger R goes off at Q28 time and the earliest time at which
Trigger Q could be simulated is at P31 in that minor cycle. The system
then behaves as though Trigger R had never been stimulated, and waits for
the next signal from point C, a Major Cycle later, to stimulate Trigger R
again. Unless CMI has ceased by then, the second attempt will also be
abortive. Only when the current Magnetic operation has finished and CMI
come to an end, will a pulse from point C be allowed to bring Control into
normal operation in obeying the Instruction which has up to then been
circulating vainly in TS COUNT.
It may not be clear why PbD6 Is needed at all; the operation des-
cribed above could have been equally well achieved by taking CMI signal
directly to clear Trigger R. However, with this arrangement an Instruc-
tion initiating a Magnetic operation would always need equal Wait and
Timing numbers, an irksome restriction for the programmer. The point is
that as soon as Transtim comes on for such an Instruction, the Magnetic
operation starts; since the Instruction at that time on the IS Triggers
is one specifying a Magnetic operation, CMI signal starts immediately.
If this were allowed to clear Trigger R by itself, Trigger Q would never
NS-y-37/11-57
come on to initiate TCI signal and call in the next Instruction; the
only way round this would be for Trigger Q to have already come on before
the start of Transtim, and this requires equal Wait and Timing numbers.
The introduction of PbD6 gets over this difficulty, since the PbD6 signal
always occurs before the start of Transtim and thus before the start of
the CMI signal due to the Instruction which itself initiated the current
Magnetic operation.
The connection marked "Request Stop" in Figure 6.12 will be explained
later.
TRIGGER TCI
Figure 6.13 shows the connections from Trigger Q to Trigger TCI, and
the output signals of the two triggers. Trigger D, also shown in the
diagram, is associated with the Discrimination facilities; for the
present, it will be assumed to be always off. With this assumption, the
relation between Triggers TCI and Q is exactly the same as that between
Triggers TT and P except that the operating signal comes at the back edge
of Q32, not at P32. Trigger TCI comes on at the end of the minor cycle
in which Q is stimulated, and goes off at the end of the minor cycle in
which Trigger Q is cleared. These two minor cycles, m+T+1 and m+T+2 are
adjacent, so that TCI stays on for only one minor cycle, m+T+2 as
required.
CONTINUOUS TCI
A key on the Control Panel labelled "Cont TCI" injects (when
depressed) a continuous signal at the output of Trigger Q. This causes
TCI to commence at the next Q32 (back) and to continue.
TRIGGER GO (FUNCTION)
From Figure 6.8 it is clear that if Trigger GO is off the signal
from "C" will fail to stimulate Trigger R, and that this in turn will
prevent the "D" signal from stimulating Trigger Q. Transtim signal is
not applied to carry out the wanted Transfer, nor does TCI signal arrive
to let the next Instruction into TS COUNT. The present Instruction
remains in possession, and pulses emerge every Major Cycle from "C"
and "D", ready to do their jobs as soon as a signal arrives from Trigger
GO. When Trigger GO is finally stimulated, the Instruction is obeyed;
all the minor cycles of action are correct, but everything happens
a fixed number of Major Cycles after it would otherwise have occurred.
Since the only effect of Trigger GO is on the signal from "C" which
occurs at some P22 time, the state of the trigger at any other time in a
minor cycle is immaterial. It will be seen that Trigger GO is cleared in
the course of obeying each Instruction, and has to be stimulated by some
means for each succeeding Instruction before it can be obeyed.
NS-y-37/11-57
Trigger GO, with the associated Trigger STOP is used to influence
the action of Control from outside by means of three of the keys on the
Control Panel (and also by means of operations of the Punch and Reader,
as will be seen). The P32 or "go" digit of the Instructions is also
concerned.
One of the Control Panel keys, the "Stop key". has three positions
called "Normal", "Stop" and "Augmented Stop". In the Normal position a
digit "1" in the P32 position of an Instruction entering TS COUNT is
allowed to stimulate Trigger GO. In a sequence of such Instructions,
Trigger GO will be stimulated once for each, and operation will be normal
as already described until an Instruction is reached whose P32 digit is
zero (called a "Stop Instruction" or "Stopper"). This Instruction stays
in suspended operation until a stimulus, called a "Single-Shot", is
supplied from outside to stimulate Trigger GO.
With the Stop Key In the Stop position, the P32 digit of the Instruc-
tion is no longer allowed to stimulate Trigger GO. As a result, all
Instructions are treated as Stop Instructions, and a Single-Shot signal
must be given for each.
The Augmented Stop position of the Stop Key again inhibits the
action of the GO digit; it also brings the STOP Trigger into play. This
trigger is now stimulated by CIS signal at the start of obeying every
Instruction; it is cleared by the Go digit of a Go Instruction, but left
on if the Instruction is a "Stopper". While the Stop Trigger remains on,
Single-Shots are ineffective, and can no longer stimulate Trigger GO;
neither the current Instruction nor any of its successors can be obeyed
until Trigger STOP has been cleared. This can be done only by pressing
the second of the three Control Panel keys concerned, the "Release Key".
The net result of the Augmented Stop position is that a sequence of Go
Instructions may be obeyed, as in the Stop position, by supplying a
Single-Shot for each. As soon as a Stopper is reached, the Machine seizes
up and will do nothing. The Release Key must be pressed before a Single-
Shot will be effective in causing the Stopper to be obeyed.
The third Control Panel key supplies the Single-Shots; it can be
moved either up or down from its normal centre position. Pressing the
Single-Shot Key once gives one Single-Shot. Raising the key starts a
succession of Single-Shots at the rate of about ten a second. If the
Stop Key is in its Stop position, this gives operation at about one two-
hundredth of normal speed.
Single-Shots alternatively come from the Reader or Punch whenever a
card is passing. In either case, one Single-Shot is emitted each time a
row of the card comes level with the reading brushes or punching knives.
There are thus twelve Single-Shots for each card which passes through
the Reader or Punch. This facility is used, in effect, to slow the DEUCE to
the speed of a Hollerith machine when reading or punching numbers. To
NS-y-37/11-57
punch twelve numbers in binary form on a card, for example, the twelve
Instructions transferring these numbers to D29 are all made Stoppers.
Each of them remains suspended in TS COUNT till a card row comes into
position, when a Single-Shop signal causes it to be obeyed. punching the
number transferred on to the card. The DEUCE then proceeds at full speed
to the next Stopper and then waits for the next row of the card.
CONNECTIONS TO TRIGGERS 'GO' AND 'STOP'
The connections are shown in Figure 6.14. The P32 digit of the
Instruction is taken from the normal NIS Gate of TS COUNT to stimulate
Trigger GO and from the normal Source Gate to clear Trigger STOP. In
all other circulation units, Source Cathode signal (and NIS Cathode signals
where the NIS Cathode is used at all) is permanently applied so that only
the selection of the appropriate Source (or NIS) number is needed to bring
the gate into operation. In this case, however, these signals are
applied only at Q32 time, and can operate only to release the P32 digit on
to HWE or IHW respectively. The actual operation of the two gates is done
by direct connections from the Stop Key to the points where the signals
from the NIS and Source trees respectively are normally applied. With the
key at Normal, the NIS Gate is always operated and lets every Go digit
through to stimulate the GO Trigger; in the Augmented Stop position the
Source Gate releases every P32 digit in an Instruction to clear Trigger
STOP. When the key is at Stop, neither gate is operated.
The connection from the Augmented Stop position to the Source Gate,
by the way, has no operational justification; it could equally well be
replaced with a permanently applied signal. The arrangement adopted,
however, permits a simplification in the electronic realisation of the
logical diagram. The point is that the same Q32 signal is used alter-
natively to operate the NIS Gate (Normal position) to do nothing (Stop
position) or to operate the Source Gate (Augmented Stop position). If
this signal were used permanently in the Source Gate whatever the position
of the Stop Key, a second Q32 signal would have to be supplied to operate
the NIS Gate in the Normal position. (These remarks can be fully under-
stood only by reference to the electronic circuits concerned).
For any Instruction to be obeyed, Trigger GO must be stimulated,
either by a Go digit or by a Single-Shot. At the end of obeying each
Instruction, Trigger GO is cleared by a Q16 in the TCI minor cycle, the
minor cycle in which the next Instruction enters TS COUNT. This is
necessary in case the next Instruction is a Stopper or the Stop Key is in
the Stop or Augmented Stop position. It also has the effect of prevent-
ing Transtim during the Set-up minor cycle which immediately follows that
of TCI. Figure 6.15 shows the relevant signals. Trigger Q is cleared at
Q22 in the TCI m.c., clearing Triggers R and P (if it is still on) at
the same time. Trigger R cannot immediately be stimulated by any signal
at point C because Trigger GO is now off. Trigger R is therefore still
off at the end of this minor cycle, and Trigger TT is then cleared; TT
NS-y-37/11-57
cannot be restimulated until the next P32 time, which occurs at the end of
the Set-up minor cycle.
The Go digit is taken to Trigger GO from the NIS Gate which comes
after the Destination Gate, rather than from the Source Gate which comes
before it because Trigger GO would otherwise be stimulated by the Go digit
of the previous Instruction. Furthermore, this arrangement avoids wasting
a Major Cycle in the operation of a Go instruction with zero Wait number.
For such an Instruction, the first signal from point C occurs while the
Instruction word is emerging from TS COUNT for the first time (the Set-up
minor cycle). If Trigger GO were not stimulated until the end of this
minor cycle, the first opportunity of stimulating Trigger R would be
lost. As things stand, Transtim signal starts immediately at the end of
the Set-up minor cycle.
It would appear at first sight that it does not matter at which point
in the minor cycle a Single-Shot arrives to stimulate Trigger GO. It
would be unfortunate, however, if this signal arrived between P16 and P22
in the TCI minor cycle, for this might allow Trigger R to be stimulated at
P22 in this minor cycle, which would cause Transtim signal to occur
during the Set-up minor cycle, while the Source and Destination numbers
were changing. All this would only happen, of course, if a Single-Shot
were applied while the Machine was doing a sequence of Go instructions
with the Stop Key at normal; while this contingency is unlikely, it could
arise and must be provided for. The provision made is to arrange that a
Single-shot, at whatever time it originates, can supply a pulse to stimu-
late Trigger Go only at Q32 time. This is the object of the two triggers
shown in the path from the point SS (the Input of Single-Shot signals from
outside) to Trigger GO. The detailed operation of these will be described
in the Circuit Manual, since the reason for having two triggers rather
than only one is purely electronic.
It has been said that the connection from the Augmented Stop position
of the Stop Key to the TS COUNT Source Gate is irrelevant; the effective
connection from Augmented Stop is the one which permits CIS signal to
stimulate Trigger STOP just as each successive Instruction has entered
TS COUNT. If this is a Go instruction, its P32 digit will come out of the
Source Gate to clear Trigger STOP; the action from then on will be just
as though the key were in the Stop position. If, however, the Instruction
is a Stopper, the Single-Shot signal cannot get through to stimulate the
GO Trigger until Trigger STOP has been cleared by pressing the Release
Key. More accurately, the STOP is cleared when the Release Key
is allowed to return to its normal position; otherwise, if a stream of
Single-Shots were being applied, several Stop Instructions might be obeyed
in the Interval between pressing the Release Key and releasing it.
It will be noticed that Trigger STOP is not cleared by a Go digit
until the end of the Set-up minor cycle, This cannot cause any waste of
time because two successive Single-Shots are never closer together then
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about 15 millisec (the interval between successive rows of a card passing
through the Reader). The complete result of an effective Single-Shot,
carrying out one current Instruction and taking the next into TS COUNT,
can never occupy more than three Major Cycles,
The GO and STOP Triggers each operate a lamp on the Control Panel
which shows whether they are on or off.
DISCRIMINATION FACILITIES
The input arrangements to Trigger D, which are shown in Figure 6.16
incorporate two special Destinations, D27 and D28. An Instruction using
either of these Destinations may cause Trigger D to be stimulated during
the course of the Transfer; this will have the effect of modifying the
action of Trigger TCI, so that it is no longer exactly as has been
described.
Assuming, for the moment, that there is no input signal at either
"DN" or "DF", the digits appearing on HWL will always he applied
effectively to gate K. If D28 is used, any signal on HWL during the
Transtim period will pass through gate K to stimulate Trigger D. In other
words, a sequence of numbers transferred to D28 will have no effect if
they are all zero, but will stimulate Trigger D if any of them contains a
digit "1".
The action of D27 is similar, but In this case, Transtim signal has to
pass through gate L, and reaches gate K only at Q32 time of every minor
cycle for which it is applied. A sequence of numbers sent to D27 will
stimulate Trigger D if, and only If, the 32nd digit of one or more of the
numbers is a "1". In the Signed convention, this means that D is stimu-
lated if any of the numbers is negative, but not if they are all positive.
DN and DF are connections from a control panel key. Raising this
gives signal on DF and ensures that Trigger D will not be stimulated by
any transfer to D27 or D28. Lowering the key gives signal on DN and
ensures that any transfer to D27 or D28 will stimulate Trigger D. The
key is used in program testing.
EFFECT OF TRIGGER 'D'
Figure 6.17 shows the output signals of Triggers R, Q, D and TCI at
the end of an Instruction using D27 or D28. The full and dotted lines
give respectively the cases where Trigger D has and has not been stimu-
lated. In both cases, Trigger Q comes on at P31 in m.c. m+T+1, and goes
off, together with Trigger R, at Q22 in m.c. m+T+2. Trigger D is cleared
by the first Q19 signal after Trigger R is cleared, that is at Q19 in
m.c. m+T+3.
Trigger TCI is stimulated at the end of the first Q32 signal after
Trigger Q comes on, that is at the end of m.c. m+T+1. At the end of each
NS-y-37/11-57
subsequent minor cycle, since Trigger Q is now off, a pulse signal is
applied to gate M (Figure 6.16), with the intention of clearing Trigger
TCI. If Trigger D is off, this succeeds at the first attempt, giving the
normal operation already described; when Trigger D has been stimulated
during the Transfer, however, it is not cleared till midway through m.c.
m+T+3; it therefore inhibits the first of the signals at gate M and TCI
is not cleared until the end of m.c. m+T+3.
Trigger D has no effect on the operation of Trigger TT, or on the IS
triggers. Thus the final effect of these facilities is that if a non-zero
number is transferred to D28, or a negative one to D27, TCI is applied not
only for its normal period of one minor cycle, but also for the minor
cycle immediately following.
EXTRA MINOR CYCLE OF TCI
Each Instruction specifies its successor by means of its NIS and T
numbers. Normally, this is determined uniquely, and the next Instruction
is the word stored in m.c. m+T+2 of DL"N". This word, which we shall call
"NIA", is let into TS COUNT by the application of TCI signal for the
minor cycle m+T+2, at the end of which the TCI gate is closed, trapping the word
NIA in TS COUNT.
When as the result of an Instruction using D27 or D28, Trigger D is
stimulated during the Transfer, TCI signal is applied also for the succeed-
ing minor cycle, m+T+3. During this second minor cycle, the successive
digits of NIA emerge from TS COUNT, return to the TCI gate, and are
inhibited; meanwhile, entering TS COUNT are the digits of the word
stored in m.c. m+T+3 of DL"N", which will be called "NIB". When TCI ends,
therefore, the word trapped in TS COUNT is not NIA but NIB.
An Instruction which transfers a number to D28, thus has the function
of choosing between two possible Instructions to succeed it. If the word
being transferred is zero, the next Instruction is NIA, the word stored
in DL"N", m.c. m+T+2; if the word transferred is non-zero, the next
Instruction is NIB, the word stored In DL"N", m.c. m+T+3. For instance,
the Instruction "16-28" will be followed by different succeeding Instruc-
tions depending on whether or not the number in TS16 is zero.
PRECAUTIONS
It is intended that the effect of an Instruction which stimulates
Trigger D shall be simply to add one to the effective value of the Timing
number, as far as it concerns the selection of the next Instruction. In
other words, NIB is to be taken as the next Instruction, and NIA is to be
completely ignored. However, NIA actually enters TS COUNT, and emerges
from it, in m.c. m+T+3, into the circuits which interpret Instructions
and generate the required signals. In order to achieve the required
result, some special precautions must be taken to ensure that no part of
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NIA is obeyed as an Instruction as it emerges from TS COUNT.
During m.c. m+T+3, the successive digits of NIB are flowing from the
NIS gate of DL"N" along IHW to the TCI gate, and entering TS COUNT. If
the digits of NIA, at that time emerging at "N", were permitted to affect
the IS triggers, they might alter the selection of the NIS gate, replacing
part of NIB with the word in the corresponding minor cycle of a different
Delay Line. The fact that TCI signal is still present is therefore used
to inhibit the digits at "N" before they can be used to generate the IS
signal (see Figure 6.6).
If the Go digit of NIA were "1", it would stimulate Trigger GO, in
spite of the fact that NIB might be a Stop Instruction. If the Wait
Number of NIA were zero, a pulse would emerge at "C" during m.c. m+T+3,
which would tend to stimulate Trigger R. Both these points are met by
the fact that, since TCI is still on, Trigger GO is cleared at Q16 in that
minor cycle. (see Figure 6.14). This leaves NIB to restimulate GO, or
not, depending on the value of its Go digit; it also prevents the pulse
(if any) at "C" from stimulating Trigger R, since this signal can occur
only at P22 time, when Trigger GO will be off.
Again, the P16 digits of NIA and NIB might be "1" and "0" respective-
ly; Trigger S would be stimulated by NIA passing through Control, and
must be cleared somehow to allow NIB to operate properly. This is done by
the CIS clearing connection to Trigger S (Figure 6.10) which leaves
Trigger S always off at the end of TCI signal, that is at the moment when
the Instruction actually to be obeyed has finished entering TS COUNT;
this Instruction then sets Trigger S according to its own P16 digit.
SELECTOR TREES
The function of a Selector Tree has already been described. Any
further explanation of the NIS Tree will be left for the Circuit Manual.
Each of the other two Trees, however, really consists of two Selector
Trees of this type: the HWE and TT connections are, in fact, more
complex than has yet been shown, though their function has been accurately
represented.
SOURCE SELECTOR TREES AND HWE
The details of the HWE connections and the two Source Selector Trees
are shown in Figure 6.18. The HWE points from the 32 Source gates, pre-
viously shown as all connected together, are really connected in four
groups of eight; the HWE points from S0 to S7 are connected to HWE0,
those from S8 to S15 are connected to HWE1, those from S16 to S23 are
connected to HWE2, and those from S24 to S31 are connected to HWE3.
Similarly, the SC connections are also made in four groups of eight,
these connection points being called SC0, SC1, SC2 and SC3. Of the five
IS triggers corresponding to the Source number of the current Instruction,
NS-y-37/11-57
the first three are connected to the First Source Selector Tree, and the
last two to the Master Source Selector Tree. Each of these Trees always
gives an output signal on just one of its eight or four possible output
lines, depending on the binary number represented by the signals supplied
from the IS triggers. Each of the eight output lines from the first tree
is connected to four Source gates, one in each group; thus HWE0, HWE1,
HWE2 and HWE3 each carry a sequence of digits from one of the Sources in
its group. Each is presented at one of four Master Source gates, one of
which is opened by a signal from the second tree to release the corres-
ponding signal into the main Highway.
As an example, suppose the Source number in the current Instruction
is 23, represented by the sequence of pulses 11101. The first three
digits go to the first tree, giving a signal on the output line connected
to S7, S15, S23 and S31. All these Source gates are opened, the signal
from S7 (the words in DL7) appearing an HWE0, that from S15 (TS15) on
HWE1, that from S23 (TS14 ÷ 2) an HWE2, and that from S31 (ones) on HWE3.
The last two digits of the Source number are applied to the second tree,
which gives a signal on the output line connected to Master Source gate 2,
allowing the pulses on HWE2 to pass to the main Highway. Thus the setting
of the number "23" on the IS triggers carrying the Source digits releases
the signal at Source gate 23 on to the main Highway, the same result as
achieved by the simpler system shown before. The more complicated system
is used because it gives more reliable operation in practice. However,
there is now no single line carrying a signal which can truly be called
"S23". In future the selector signal will be called, for example "S7(23)",
since only the simultaneous application of signal at "S7" and at output
"2" of the Master Scarce Tree will release the signal from "Source Gate
23" on to Highway.
DESTINATION TREES AND TRANSTIM
A typical Destination gate is shown in Figure 6.19, as a reminder;
the dotted connections refer to storage positions, where the Destination
gates act as changeover switches. The "TT" points of all 32 gates were
previously shown joined together; in practice, however, these points are
joined only in four groups of eight. The arrangement, similar to the HWE
connections to Source gates, is shown in figure 6.20. The inputs from
Triggers IS13 and IS14 determine to which of the lines TT0. TT1, TT2 and
TT3 Transtim signal shall be routed when it appears.
If the Destination number of the current Instruction is 13, for
example, Destination Selection signals are applied to the Transtim gates
of D5, D13, D21 and D29; when Transtim signal is applied, it is routed
to the line TT1 and opens only the gate of D13. Again, the new notation
will now be adopted of calling the Destination selection signal, for
example, "D5(13)".
NS-y-37/11-57
PROGRAM DISPLAY
Two special facilities are provided for testing new Programs. One of
these is called Program Display; it involves connections to Control,
Trigger PUNCH and the Output Staticiser (D29). The circuit is shown in
Figure 6.21. Trigger H, which is stimulated by CIS at the moment when
each new Instruction has finished entering TS COUNT and is about to start
emerging at "J", is a special type of trigger which automatically clears
itself a fixed time (in this case, about 40 microsec) after it has been
stimulated. The return path through the 40 microsec delay has been
inserted for logical completeness, and has no particular electronic
equivalent. The signal from Trigger H covers the minor cycle while each
Instruction first emerges from TS COUNT, and part of the next m.c. The
digits covered in the second m.c., however, are identical with those in
the first, since Trigger H clears itself before the second appearance at
"J" of P16, the first digit affected by the Unit Subtractor.
The output of gate "P" is thus a copy of each successive Instruction,
just as it entered TS COUNT, with a second copy of the first few digits.
Normally, this does not pass gate "Q", and has no effect on the operation.
There is a key on the Control Duel labelled "Program Display"; if
this key is down and the Stop Key is in the Augmented Stop position, a
signal is applied at the point marked "PD". This signal has three imme-
diate effects. Firstly, it stimulates Trigger PUNCH, so that cards run
continuously through the Hollerith Punch; this provides a Single-Shot
signal as each row of a card passes the punching station, causing succes-
sive Instructions to be obeyed only in time with the successive rows (since
we are at Augmented Stop). Secondly, it inhibits any words which might be
sent to D29 by an Instruction from reaching the OS and being punched;
such an Instruction is therefore "obeyed" in its turn, but has no practical
effect. Finally, it sends to the OS the signal from gate "P", which
consists of a copy of each successive Instruction in the order in which
they are obeyed; the second copy of some of the digits has no effect,
tending merely to restimulate those OS triggers put on by the first copy.
The complete effect of the "Program Display" key is that the program
is carried out normally, but at a speed determined by the Hollerith Punch.
Instead of displaying or punching any results of the computation, however,
all the Instructions are punched in the order in which they are obeyed.
It is arranged that when the STOP Trigger comes on it inhibits the action
of the Program Display Key. Thus when a Stopper is reached in the course
of doing Program Display, the Punch stops and no further progress is
possible until the Release Key is pressed and Program Display restimu-
lated.
REQUEST STOP (FUNCTION)
The second special facility for testing new programs is called
Request Stop. When in use, is causes the computer to stop automatically
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as soon as an instruction enters TS COUNT which has a previously specified
Source, Destination or NIS number, or any combination of these. Different
settings of keys, for example, will cause the computer to stop as soon as
it reaches an instruction with NIS 5 (S and D irrelevant) or an instruction
"13-27" (NIS irrelevant).
The operation of Request Stop involves additional functions of the
External Tree key and the 14 IS keys and three special Request Stop keys
labelled "NIS", "S" and "D" respectively. Request Stop is brought into
action by raising the External Tree key and pressing the appropriate
selection of the three special keys; the selected NIS, Source and
Destination numbers will be those currently set on the IS keys. Thus, if
the IS keys are set at "5, 13-27", the relationship between the form of the
stopping instruction and the setting of the Request Stop key is as follows
("n, 13-d", for instance, means that the computer will stop as soon as it
reaches an instruction with Source number 13, independent of the NIS and
Destination numbers):-
Request Stop keys down Stops at first instruction
of the form
Source only n, 13 - d
Destination only n, s - 27
NIS only 5, s - d
Source and Destination n, 13 - 27
NIS and Source 5, 13 - d
NIS and Destination 5, s - 27
All three 5, 13 - 27
Thus, if one key is already down, pressing a second and a third makes
the computer less likely to stop, since it increases the speciality of the
instruction form needed to stop it. If none of the three Request Stop
keys is down, the computer will not stop, even though the External Tree
key is in the up position.
It world perhaps be more correct to describe the computer as "inter-
locked" rather than "stopped" by Request Stop. Trigger GO remains on, and
action is suspended only so long as conditions for stopping are maintained;
if the relevant IS keys are moved, or External Tree key returned to normal,
the computer immediately proceeds.
REQUEST STOP (MECHANISM)
Request Stop works by injecting a signal at the CMI input to Control
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whenever conditions for stopping are fulfilled. While the signal is
present, Trigger R is stimulated every major cycle and cleared 6 microsec
later at PbD6 time, before Trigger TT or Trigger Q has had time to come
on. The instruction in suspense is thus not obeyed until the Request
Stop conditions are removed. However, it will be seen in the next chapter
that the Destination Triggers functions are operated by PbD6, and not by
TT. It is therefore unsound to interlock on an instruction with Destina-
tion number 24 (Destination Triggers), since the instruction would be
repeatedly obeyed, once every major cycle, while waiting in TS COUNT.
The connections for Request Stop are Shown in Figure 6.22. If
External Tree key is up and one or more of the Request Stop keys down, a
signal is injected at the CMI input to Control unless it is inhibited by
non-fulfilment of the relevant condition.
The state of the IS triggers is sampled by a set of 14 not-equivalent
gates; each of these gives out a signal if the corresponding IS trigger
and key are in opposite states. The first three of these signals are
combined in a one-gate, which thus gives a signal at point N unless the
instruction in TS COUNT has a NIS number equal to that set on the first
three IS keys. Similarly, there is a signal at points S and D respectively
unless the Source and Destination numbers in TS COUNT correspond with
those on the IS keys.
The three signals at points N, S and D are switched by their respec-
tive Request Stop keys into a common one-gate, which thus gives a signal
at point R if there is any discrepancy in the selected parts of the
instruction between the word in TS COUNT and the IS keys.
If the External Tree key is up and one or more of the three Request
Stop keys is down, a signal is generated at Point S. This signal passes
to the CMI input to Control unless it is inhibited by a signal at Point R.
Thus, to sum up, a signal is injected at the CMI input to Control if, and
only if, there is complete agreement between TS COUNT and the IS keys
over the selected portions of the instruction word.
The inhibiting action of a signal at the CMI input to Control has
already been described in the paragraph on Control-Magnetics Interlock.
COMPLETE DIAGRAM OF CONTROL
Figure 6.23 gives a complete logical diagram of Control excluding
the IS Triggers, the Selector Trees, and the detailed Request Stop
arrangements.
NS-y-37/11-57
DESTINATION TRIGGERS
D24 is used for various assorted operations about the Machine which
have in common only the fact that none of these operations requires the
transfer of information through the Highway.
The connections are shown in Figure 7.1. In contrast with all other
Destination Gates, D24 operates, not on Transtim, but on the brief PbD6
signal which occurs shortly before the start of Transtim. The object of
this is to ensure that, in spite of any accidental circuit delays,
Triggers MULT and DIV are always brought on at least by the beginning of
the minor cycle in which the Instruction stimulating them is officially
obeyed.
Since Transtim is not used, a dummy D24 Destination Gate is inserted
to provide an alternative path for the Transtim signal, which would
otherwise divide itself among other Destination Gates (see circuit manual
for precise operation of Trees and Gates).
Which of the twelve possible operations is required is specified by
the Source number of the Instruction, that is by the setting of the IS
Triggers corresponding to P5, P6, P7 and P8 (P9 is not used, since the
twelve operations required can all be accommodated within the first 16
Source numbers). The PbD6 signal gated by D24 is first routed to one or
other of two groups of 2-gates, according to the state of IS8, to the
group of eight numbered 0 to 7 if the P8 digit is “0” and to the group of
four numbered 8, 9, 10 and 12 if the P8 digit is “1”. The Instruction
"11-24" is not used because it could cause complications with Control-
Magnetics Interlock if a Magnetic operation were in progress at the time
(see the chapter on Magnetics).
Within each of the two groups of 2-gates, selection is done by con-
nections from the First Source Tree. For example, if the Instruction were
“18-24”, the First Source Tree would give signal only on its “O” output
line, not on the other seven; the PbD6 signal would be routed first to
the group of four 2-gates, since the P8 digit is “1”, and then by the Tree
output to Gate 8 to clear the OS.
The twelve functions of Destination Triggers are set out below:
Instruction Effect
0 – 24 Stim MULT
1 – 24 Stim DIV
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These initiate multiplication and division as already partially
explained
2 – 24 TIL Discrim
When reading or punching, it is often desirable to distinguish the
last row on a card from its predecessors; this row is therefore marked
by a special signal called TIL (twelfth impulse line) which is issued by
the Reader or Punch respectively for a period covering the time when the
twelfth row is under the reading brushes or punching knives. To achieve
the object of following a different course of action after the twelfth
row from that pursued after the others this TIL signal must be connected
to D28 which discriminates between zero and non-zero numbers. Since TIL
is not wanted for any purpose other than connecting to D28 this connec-
tion is made automatically by the Instruction "2-24"; this avoids the
necessity of allocating a special Source number to TIL.
3 – 24 Stim TCA
4 - 24 Clear TCB
5 – 24 Stim TCB
TCA and TCB are trigger circuits which modify the action of certain
Sources and Destinations; they will be described subsequently
6 – 24 Clear ALARUM
7 – 24 Stim ALARUM
Many programs incorporate arithmetic checks on their own operation;
the failure of such a check is most conveniently indicated by operating
the Alarum. This sounds a buzzer and lights a special red lamp on the
Control Panel
8 – 24 Clear OS
It is necessary to clear the OS between displaying successive words,
since otherwise all those lamps would remain lit which had corresponded
with a digit “1” in any of the words displayed.
9 – 24 Clear PUNCH and READ
10 – 24 Stim PUNCH
12 – 24 Stim READ
NS-y-37/11-57
LOGICAL OPERATIONS UNIT
Associated with TS14 and TS15 are four extra Sources, S23 to S26. If
one of these Sources is selected, the digits released onto the Highway
will represent some special function of the numbers in either one or both
of the