Page:Alan Turing - Proposed Electronic Calculator (1945).pdf/25

 TS 11 will usually be used in connection with error calculations, and accordingly has a special role in the production of multipliers.

TS 12 is used for the timing in ‘automatic’ multiplication and for the selection of unusual combinations of digits in the multiplier. The word ‘automatic’ is used because of an analogy from desk machines.

To decide between types K to T we use CI 5-8. Digits 5,6,7 are treod out to the valve elements TRG 000 TRG 111, as in Fig. 23. These tree elements are each associated with two types, which are distinguished by CI 8. Thus TRG 000 would be identical with KvL if it were not for timing. For this timing we introduce CATIM which is to be stimulated during the appropriate time in CA operations. KvL is identical with TRG 000 & CATIM (Fig. 24).

In case K we pass the output of TS 6 to COMMIN and hence to the inputs of all the delay lines. We gate the appropriate one of those at the appropriate time, given by TIMCA by comparison of the output of the slow counter SCA with CI.

In case L we do somewhat similarly, passing the appropriate output to COMMOUT and thence to the input of TS 6 at the appropriate time given by TIMCA.

In case M we gate the appropriate output and pass into TS 6.

In case N we pass the output of TS 6 to the inputs of the other TS, only gating the one required.

In case O the first effect is to set the mechanism in motion to pass a card through the reproducer. By means of a commutator arrangement or otherwise the reproducer sends back a series of pulses which indicate the times when the reproducer punches are ready to accept current. In the circuit diagram (Fig. 25) two sets of pulses are shown which are intended to mark the beginnings and ends of these periods. They may be separately provided by the reproducer, or one may be derived from the other by delaying or otherwise. The two sets of pulses each control trigger limiters connected up so as to extinguish one another. (Do not confuse this with the two mutually extinguishing triodes that will normally form part of a trigger circuit or trigger limiter.) One of the trigger limiters TIMOUTCARD stimulates the trigger circuit OUTIM on the first admissible P 10. A pulse on the stimulation of OUTIM goes into a slow counter SCB and enables us to keep track of the number of rows of the card that have been punched. The content of SCB is compared with that of SCA and when they agree we know that the minor cycle which we wish to pass out is now available, and TIMCA is accordingly stimulated. TIMCA and OUTIM together permit COMMOUT to pass out to the trigger circuits OUT 1 OUT 32 on which it is set up statically and controls the punches.

On the final exit of the card the reproducer sends back a signal to the calculator, which, in combination with O operates a trigger limiter CARDEXOUT. This suppresses CATIM and hence O. CARDEXOUT has feedback to suppress itself, and this will be successful because O will have been suppressed by the time it comes to act.

The behaviour in case P (input) is very similar. The chief difference is that whereas OUTIM was used to gate the output from the calculator INTIM is used to gate the input. It/