Patent GB-741418-A (GB)
Title: Improvements in or relating to electric adding and subtracting devices
IPC: G06F7/50
Filed: 1952-03-17
Abstract: 741,418. Digital electric calculating-apparatus. SOC. D'ELECTRONIQUE ET D'AUTOMATISME. March 17, 1952 [March 17, 1951], No. 6917/52. Class 106 (1). In an electric device for adding and subtracting numbers represented by binary seriesmode pulse trains, comprising half-adders 1, 2, Fig. 1, one output train B and partial-carry output trains R1, R2 (delayed where necessary) are applied to the half-adder 1 (inputs 3 and 4) from which are derived a partial carry output train R1 and a net partial-result pulse train (B+R) n  (or corresponding potentials), and the latter is applied together with the other input train A (inputs 10 and 9) to the half-adder 2 from which are derived either an addition or a subtraction partial carry output train R2, under control of selective switching means, and a final (sum or difference) output train S. In the device illustrated in Fig. 1, the combined carry train R=R1+R2 is delayed at 8 by one digit pulse period # before being applied to the halfadder 1. In the device shown in Fig. 3, part of the delay means is incorporated in the halfadders. The pulse train B (positive pulse for " 1," no pulse for " 0 ") is reshaped in tube 70 by timing pulses T from a programme circuit, The anode output pulses from tube 70 and the carry output pulses R1 from tube 74 and R2 from tube 75 or 76 (for addition and subtraction respectively) are applied to a delay network 72 in which they are reflected at the short-circuited end and supplied with reversed polarity, after a delay 6/2, to an output tap connected to a resistor 93 in the control-grid circuit of a tube 77. From an intermediate tap the pulses are supplied also to an amplitude-discriminating tube 79 which, if it receives a double-unit input pulse, delivers a negative output pulse which temporarily flips over a trigger circuit 83,84 from its single stable condition thereby applying a positive potential from the anode of cut-off tube 84 to the suppressor grid of carry-forming tube 74, and a negative potential from the conducting tube 83 to resistor 92 which prevents the pulse subsequently applied to resistor 93 from being transmitted through tube 77, the pulses T being applied to this tube with a phase shift #/2. The tube 77 thus delivers an output pulse to a tap 96 on delay network 97 if there is a pulse in the B or R train but not both. The pulse train A, reshaped in tube 99, is supplied to the input tap 98 (spaced by 6/2 from 96) of the network 97 which has two output taps connected to a second half-adder circuit 77<SP>1</SP>, 79<SP>1</SP>, 83<SP>1</SP>, 84<SP>1</SP>, and carry-forming tube 75, similar to the first. The output of tube 77 is applied also, through network 100 of delay 6/2, to the control grid of subtract-carry-forming tube 76, thereby producing, during subtraction, an output pulse except when trigger 831, 84<SP>1</SP> is actuated. The tube 75 or 76 is operative according to the condition of an add/subtract bi-stable trigger circuit 40, 41 having connections to the tube screen grids. In an alternative (Fig. 4, not shown), the tubes 79, 79<SP>1</SP> and triggers 83, 84, and 83<SP>1</SP>, 841 are' replaced by coincidence-detecting gate tubes. As shown in Fig. 5, each halfadder comprises a bi-stable trigger circuit 129, 130 or 129<SP>1</SP>, 130<SP>1</SP> which counts the input pulses applied with appropriate phase shifts during a pulse period, the device being controlled by four series of timing pulses relatively shifted by 6/4. The B and R pulses, if present, are supplied from tubes 126,127 at instants 0, #/4 respectively to the trigger 129, 130 which is reset at instant 36/4 by a negative timing pulse at 131. If an R pulse at 6/4 returns the trigger to the rest condition (tube 130 conductive), indicating a count of two, a positive carry pulse is sent through a capacitative connection to the control grid of tube 132, the output of which after delay by # and inversion in network 140 is applied to input tube 127. If the trigger is in its actuated condition, indicating a count of one, at instant #/2, an output pulse is sent through tube 133 to trigger 129<SP>1</SP>, 1301 to which the A pulses are applied at #/4 via inverting tube 135, delay network 136 and pulse shaper 134. The addition and subtraction carry-forming tubes 1321, 138 are controlled from opposite sides of trigger 129<SP>1</SP>, 130<SP>1</SP> as well as from trigger 40, 41, and their outputs are connected by lead 142 to a tapping on network 140 such that a delay of 3#/4 is provided. The output pulse train is delivered from tube 133<SP>1</SP> at instants 30/4. Further devices are described in which the first half-adder only is similar to that of Fig. 5, the second half-adder comprising, for example, a double-triode switch 180 controlled by a tube 179, Fig. 9, to which positive A pulses are applied, shifted by #/2, from inverting tube 151, and a switch 176 controlled by a tube 177 to which a positive pulse is supplied at each instant 6/2 if the device is set for subtraction. The switches 176, 180 selectively apply earth potential from their conducting triodes (indicated by shading) through rectifiers to the lower ends of resistors 169-171. In the rest condition shown, resistor 169 only is unearthed, whereby if trigger 129, 130 is in its actuated condition a positive potential will be applied through cathode follower 167 to the control grid of output tube 133 to which timing pulses are applied at 147. If, however, an A pulse is present, 180 is switched over and resistor 170 only is unearthed so that the positive potential is applied to carry-forming tube 132<SP>1</SP> (138); if, also, trigger 129, 130 is in the rest condition, an output pulse will be produced from tube 1331, the suppressor and control grids of which are connected to the anodes of tubes 129 and 151 respectively. The switching over of 176 during subtraction, causes a carry to be produced in tube 132<SP>1</SP> only when an A pulse is not present.