Patent GB-826614-A (GB)
Title: Improvements in or relating to electronic digital computers
Inventor: GILLIES DONALD BRUCE
IPC: G06F15/78
Filed: 1955-01-24
Abstract: 826,614. Electronic digital computers. NATIONAL RESEARCH DEVELOPMENT CORPORATION. Jan. 20, 1956 [Jan. 24, 1955], No. 2037/56. Divided out of 826,613. Class 106 (1). In an electronic digital computer " overflow " of an answer-representing number signal from the computing circuit (mill) beyond the range of numbers capable of being represented by the form of electric signals used, effects a control of the manner of subsequent operation of the machine dependent upon the form of order signal currently operative in the machine. For example, during a division operation, overflow causes an immediate stoppage of the machine, while during other operations overflow merely limits the manner of operation of the machine to prevent transfer of an erroneous answer arising from the overflow to a particular register. The invention is described as applied to the machine disclosed in Specifications 826,612 and 826,613 in which 42 digit-order-words, Fig. 2 (c), are each divided into A and B orders, each of which is similarly divided in time order into M, F, X, N digits. The three M digits define the address in the accumulator register group 2, Fig. 1, of the high speed store 10, of any required modifier word to be used for altering the subsequent N and/or X digits of the same order. The six F digits define the function to be performed by the machine. The three X digits select the particular accumulator register that is to be connected to the mill 5, and the seven N digits define the address in the store 10 (accumulator group 2 or a register group 4) where one operand is to be obtained or delivered. The normal operating cycle of the machine comprises A and B, periods during which the A, B orders respectively are obeyed, followed by a C period during which the next order word is selected and fed to the control line, Fig. 4. The A, B periods each have a length of two beats (D, E beats) but other beats may be interposed between the D, E beats dependent upon the order in question. The C period is of one beat length and each beat is of 42 digit intervals length. Of the seven accumulator registers 2, Fig. 1, the first five ACR1 ... ACR5, Fig. 6a, are as described in the abovementioned Specification 826,613. The " p " accumulator register ACR6, Fig. 6b, in addition to performing normal word storage like ACR1 ... ACR5 is also used for holding one of the operands in a multiplication or division operation in a single word storage register Q15. The accumulator ACR6 also includes a computing circuit AS1, and adding circuits ADR2, ADR3 provided with a regenerative loop of variable delay time between the output of adder ADR3 and the computing circuit input whereby a right or left shift of a number circulating in the circuit may be effected for each circulation. The " q " accumulator register ACR7, Fig. 6c, is also used for holding one of the operands during multiplication or division. The thirty-two address registers 4 and auxiliary registers 3, Fig. 6d (not shown) are as described in Specification 826,613. In addition to the beat counter and various staticisors described in that Specification, hand switches smO, sml ... sn9, Fig. 9, are provided for generating an order word. These switches are set according to the respective M, F, X, N digits of a desired order, and through " and " gates W10, W11 ... W31 controlled by clock pulses T0, T1 ... T20 pass a corresponding series mode signal over line Y13 to the control line, Fig. 4, the word being fed to line Y13 via the upper or lower gate of a doubleentry-gated-delay W37 to form an A or B order according to whether a switch MS is in its shown or reversed position. General operation.-A control address number signal is continuously circulating in the control number register A01, Fig. 4. This number is fed, during the E beat of the B period during which the immediately preceding order word is being obeyed, through a double entry-gated delay A21 to one input of the adder ADR1. At standard digit time 32 a single pulse is fed through a delay A61 to the other adder input whereby the control address number is increased by unity and flows down the control line of unit delays A24 ... A48. It also flows through a 35 interval delay line A14 and mixer A12 into the register A01 where it is retained until the next following E beat of a B period. In this manner the order addresses are normally rendered operative sequentially. The unit delays A24 ... A48 provide outputs I0, I1 ... I17 which at digit time 40 (i.e. the end of the B period E beat) set up the N digit staticisors according to the new control address number which is always one of the registers in the groups 4, Fig. 2, having address numbers 64- 95. During the next beat, the C period D beat, the new order word signal from the selected address register 64-95, Fig. 6d (not shown), is, as described in Specification 826,613, fed over bus Y40 and double entry unit delay A41, Fig. 4, to the input 67 of adder ADR1 and flows down the control line A24 ... A48, whereby the M digit staticisors are set according to the A order of the order word, and, as described in Specification 826,612, select any required modifier word which is fed from a selected accumulator register to the adder input 68 to modify the N and/or X digits of the A order. The whole modified order word signal is fed back through the delay line A14 to input delay A21 whereby it circulates once in each beat time. The B order is lost from the control instruction line, and, at the end of the C period D beat, the N, X, F digit staticisors are zeroized and then reset according to the A order. The setting of the X digit staticisors selects the address of one operand from an accumulator register ACR 1... ACR7 and the setting of the N digit staticisors selects another operand from a register in any one of the register groups 2, 3 or 4. During the A period D beat, the two selected operand signals flow from the store 10 over bus-bars Y41, Y44 to the mill 5, where they are operated upon according to the setting of the F (function) digit staticisors. At the end of the A period D beat the N, X digit staticisors are zeroized and the N digit staticisors are reset by either the N or X digits of the order, dependent on the nature of the order specified by the F (function) digits, to select the register address in the store 10 to which the mill output, which becomes available as the E beat commences, shall be directed over bus-bar Y2. The order word circulating through delays A14, A21 re-enters the control instruction line A24 ... A48 at this time and during this E beat a return path is provided for the leading B order part of the circulating order word from delay A48 to input delay A41 while delay A21 blocks re-entry of the A order. Due to the shorter delay time of the operative return path, the B order is transferred in timing to that of the preceding A order, and during the B period D and E beats, the B order is obeyed in a similar manner to the operations described above for an A order. Selection of the next order word is initiated as above described during the B period E beat. Overflow arrangements.-The two operand signals arriving at the mill over bus-bars Y41, Y44 are each 42 digit number words, Fig. 2 (b), in which the sign digit (digit position 38) has been copied into the next following digit position 39, during passage from the respective registers, by double-entry-gated delays V54, V57, Fig. 6a, respectively. If the sign digit (38) and the following digit (39) of the output signal from the computer CPC, Fig. 7, differ, then overflow has occurred. These two digit signal pulses are derived (sensed) from unit delays B57, B58 in the computer output path and compared by means of gates B39, B130 and inverters B47, B49 in the right-hand gate of a double-entry -gated delay B38 which, on the occurrence of overflow is set " on " to give the overflow indicating waveform OVR, which remains on for a variable period dependent on the current order code. Similar overflow arrangements are provided in the " q register ACR7, Fig. 6c, which is used with the register ACR6 and the mill during multiplication and division. If overflow occurs in the number signal circulating in the register ACR7 during a division operation, the sign digit (38) and the copied sign digit (39) have the same value. The digits in question are derived from the outputs of unit delays Q65, Q66, in the signal circulation path and compared in a double-entry-gated delay M86, Fig. 8 (not shown), which is set " on " on the occurrence of overflow to light a warning lamp, and stops the machine by blocking the beat counter at the next C period. The detection of overflow is arranged to produce different controls according to the nature of the operation in question. Thus, the setting " on " of the OVR waveform indicating overflow within the mill may not be immediately effective, but for certain " write orders," e.g. order numbers 71, 73, the machine is stopped by blocking the beat counter and another warning lamp lighted. In some circumstances, however, the presence of overflow is legitimate and the writing of the answer signal into the main store (order 71) is permitted by reversal of a manually operated switch WS (not shown) in the beat counter circuits which precludes detection of overflow from blocking the beat counter. The detection of overflow within the mill may also be treated arithmetically by use of jump orders 64 or 65 (see below). Operation with jump orders (60-65).-The various orders (order codes), defined by the F digits, with which the machine deals are set forth in the Specification. For any jump order (60-65) the trigger circuit B18, Fig. 7, may be set " on " to provide the jump waveform J at digit time 2 of an E beat and reset " off " as the next C beat commences. The presence of the jump waveform breaks the normal machine cycle of sequential selection of order words effected normally by increasing by un