Patent GB-877192-A (GB)
Title: Apparatus for multiplying two factors
IPC: G06F7/498
Filed: 1959-06-08
Abstract: 877,192. Multipliers. NATIONAL CASH REGISTER CO. June 8, 1959 [June 27, 1958], No. 19457/59. Class 106 (1). In multiplying a mixed radix number, e.g. a sterling quantity, by a decimal number, the mixed radix number is treated as multiplier and groups of pulses representing the digits of the decimal number are applied in parallel to the orders of an accumulator a number of times representative of the digit of the mixed radix number acting as multiplier. The machine described multiplies a four-figure decimal number having the decimal point in any position by a sterling quantity not involving fractions of a penny and of up to four figures in pounds. The quantities are entered on a keyboard, the decimal point being selected by a wafer switch and the answer is both indicated and printed as in Specification 721,721. The machine is sequenced by a ring of thyratrons Ml to M22 controlling the following operations : (1) and (2) multiplication of decimal number by units and tens orders of pence by gating groups of pulses to pence accumulator; (3) and (4) multiplication, into shillings accumulator, by units and tens orders of shillings; (5) to (8) multiplication, into pounds accumulator, by units to thousands orders of pounds; (9) and (10) multiply into pence accumulator fractional part of shillings product by 12; (11) and (12) multiply, into pence accumulator, fractional part of pounds product by 240; (13) round off pence total, by adding 0.5 and neglecting resulting fraction; (14) to (17) divide pence by 12, quotient to shillings accumulator; (18) to (21) divide shillings by 20, quotient to pounds accumulator; and (22) read out and print answer. The above operations are all used only when every digit of the sterling quantity is non-zero and the decimal number is not a whole number. According to the settings of the input keyboards certain of the steps may be omitted and the corresponding thyratrons not ignited. Division is by complement addition, but the dividend is first checked that division is possible. Fig. 4B shows a logical diagram of a suggested method of division by 12 of the quantity stored in the six orders of pence accumulator 139. The circles indicate AND gates under the control of thyratrons M14 to M17 of the ring. When M14 is fired gates 178 to 180, 181 to 185 and 186 are opened and the outputs of the " 0 " stage of the sixth (highest) order, and the "0" and "1" stages of the fifth and fourth orders are passed to decision circuit 172. In the three orders being examined, the circuit 172 tests for "Not 0" in the highest, " Not 0 or 1 " in the middle order and " Not 0 or 1 in the lowest order with Not 0 in the middle order." Satisfaction of any of these three conditions indicates divisibility by 12 and a signal will issue to divisor complement generator 174 to add 988 to the three orders being considered, at the same time adding one to the appropriate order of shillings accumulator 142. When the contents of orders 6 to 4 of pence accumulator are not divisible by 12, a signal from circuit 172 extinguishes thyratron M14 and fires M15 opening a new line of gates and connecting orders 5 to 3 of the pence accumulator to circuit 172. The process continues until a number less than 12 is stored in the pence accumulator. In contrast to this method the machine described uses circuitry which stops dividing only when division is not possible rather than starting when division is possible. This is described below. Pulse generation and gating circuitry (Figs. 13 to 19, not shown, and Figs. 20 to 23, 25 and 26).-A multivibrator produces pulses and " half after " pulses named respectively 0‹ and 180‹ pulses. An A-ring of conventionally arranged gas-filled tubes is stepped by 0‹ pulses and comprises A-start, A-delay, A10 to A1, and A0-tally tubes. Each tube primes the next for firing but the A10 to A1 tubes are directly connected to a common anode voltage in such a way that once fired they are extinguished only by the firing of the A0-tally tube. Thus tube An provides a gating pulse of duration n 0‹ pulses. A B-ring of triodes Bl to B10, in which the control grid of each tube is connected to a corresponding A-tube gates 0‹ pulses on to lines B 1  to B 9  of Fig. 20. In each A-ring cycle line B n  carries n pulses. The use of B 10  is described later. A J-ring comprises gas-filled tubes J0, J-delay and J1 to J9 and is stepped by pulses from the A0-tally tube. The number of tubes of the ring actually ignited is under the control of the sterling input keyboard. If 6 is the multiplier (pence, shillings or pounds) the ring cycles until the J-6 tube is ignited, after which the M-tube then controlling resets the ring. The J-delay tube merely provides a delay to ensure resetting the ring should the multiplier be 1. A K-ring comprises cathode follower connected tubes K1 to K9 associated with tubes J0 to J9 which each gate a 180‹ pulse at the time the corresponding J-tube is fired to the sterling keyboard which passes it to the M-chain to ignite the next M-tube. Thus a 180‹ pulse appears on line K n  of Fig. 22 as the J n  tube is fired, i.e. after n groups of m pulses have appeared on line B m  of Fig. 20. Operation.-The multiplication of 03.24 by ú21 6s. 4d. is described. Since the multiplicand has two places of decimals, all wafer switches are to be assumed in position 3, following the setting of the decimal point by the operator. (1) M1 tube conductive. This is so because the 4-key 861 of the pence units order keyboard is depressed connecting the control grid of M1 through lines 421 and 416 and the shield grid through lines 835, 840, 433 and 416 to a power supply. When conductive the tube primes the next tube by applying potential to the control grid. Thus the potential at point 836 is applied through lines 835, 840, 433, the contacts 434, closed since the tens order pence key is undepressed, line 865 and line 869, since a units order shillings key is depressed, to the grid 870 of M3. Had there been no pence in the multiplier but e.g. unit shillings, then M3 rather than M1 would first have been fired through potential paths dependent on the keyboard settings. Groups of 4, 2 and 3 pulses are now selected by decimal number units, tens and hundreds keyboards respectively and passed to certain orders of the pence accumulator four times, through a pence input matrix, until the J-ring reaches the tube J4 when a pulse on line K4 is gated through depressed units pence input key 4 to fire M3. Accumulators.-One order of the pence accumulator comprising seven orders is shown in Figs. 34 and 35 and is typical of all accumulators. It comprises storage flip-flops 961 to 964 together with a transfer flip-flop 965. Input is negative pulses on line 956. A storage flipflop is on when the left-hand side is conductive, but the transfer flip-flop 965 is storing a carry when the right-hand side is conductive. If the flip-flops 961 to 964 are allotted the values 1, 2, 4 and 8 respectively the count proceeds normally with a stage being switched only on a negative output from a previous stage until a count of 8 is reached when the switching on of flip-flop 964 also causes flip-flops 962 and 963 to switch on, registering a nominal value of 14. This is due to positive feedback from point 1020 at the anode of the right-hand section of flip-flop 964 over line 1021 to the control grids 1022, 1023 of flip-flops 963 and 962. A count of 9 is registered as of value 15. The tenth input pulse on line 956 switches flip-flop 961 off and the resultant negative pulse output on line 1002 is applied both to flip-flop 962 and on line 1003 to flip-flop 964 switching it off. This eliminates the positive feedback to flip-flops 962, 963 and enables them to be switched off. A large capacitor 1025 connected across the path from point 1020 to grid 1013 ensures that flip-flop 964 remains off when the negative pulse due to switching off flip-flop 963 is received. The negative output from flip-flop 964 is applied to the transfer flip-flop 965 at control grid 1029 shifting conduction to the right-hand section. 180‹ pulses are continually applied on line 543 through an inverter 1031 and line 1041 to the right-hand sections of the transfer flip-flops of the accumulator. Thus immediately after being cocked by an 0‹ pulse a transfer trigger is reset by an 180‹ pulse. The resultant output of flip-flop 965 is applied on line 1045 through amplifier 1048 to line 1055 as input to pence No. 2 order. The count stored by a significant order of the accumulator is registered by marking one out of ten lines with a negative voltage derived by applying the output of the left-hand sections of the flip-flops through a resistance network to the lines. Additional lines 1313, 1314 also register if a count of 1 or 0 has been attained (see division). Orders 1 and 2 of the pence accumulator always represent units and tens of pence, respectively, and to allow for the decimal point the higher orders of the accumulator are used. Thus, if the pence orders are assumed arranged sequentially clockwise in a ring, the decimal point lies between the one and seven orders, decimal fraction orders proceeding anticlockwise from the point. In the present examples, orders 7 and 6 are allotted to the first and second places of decimals respectively. Inhibition of transfer &c. will appear from the following description. The groups of 4-pulses picked from the B 4  line by depression of the 4-key of multiplicand units keyboard (actually representing second place of decimals in the example being worked) are passed on line 912 to the control grid of triode 904 which reproduces the pulses on line 924 an input to the pence input matrix (Fig. 29). Line 924 is common to diodes 925, 1975 and 2377, but diode 925 has an anode potential from M1 through isolation diode 908 (Fig. 21) and line 926. Diode 926 conducts and the pulses pass through wafer switch 943, the third terminal, line 1542 to input amplifier 1544 of pence