Patent GB-661099-A (GB)
Title: Improvements in electronic adding and subtracting apparatus
IPC: G06F7/50
Filed: 1948-05-13
Abstract: 661,099. Digital electric calculating apparatus. RADIO CORPORATION OF AMERICA. May 13, 1948 [June 26, 1947], No. 13156/48. Class 106 (i). [Also in Group XL (c)] In an electronic adding apparatus employing a plurality of cascaded stages for successive binary orders, an output voltage representative of a digit of the result is obtained in each stage by combining voltages representative of the two digits to be added, a carry voltage from the previous stage and twice the carry voltage to the next stage. A complete stage is shown at 103 in Fig. 4, with preceding and succeeding stages 105, 107 and 109 in outline. The digits 0 and 1 are represented in the stage by voltages +17 and - 23 standing on lines 149, 155, the representation, however, being reversed at successive stages. The stage has a carry-over input terminal 113, from the preceding stage and two input terminals 5 and 13 for the input digits, two-way switches 21 and 29 enabling them to be connected to either of the lines 149 and 155. To produce the carry-over output voltage, the input terminals are connected through resistors 121, 123 and 125 to the grid of a carry-over triode 119 which saturates when the carry-over digit is 0, the grid then going positive, and cuts off when the carry-over digit is 1, the grid then going negative. The anode is connected by a resistor 127 to a positive line 129, and by series-connected resistors 131 and 147 to a negative line 145 so that the voltage at the junction of 131 and 147, to which the carry-over output terminal 117 is connected, tends to be less than - 23 volts when the triode saturates and greater than +17 volts when the triode cuts off. Limiting rectifiers 151, 153 hold the voltage at either - 23 volts or +17 volts representing the digits 0 and 1, respectively, in the next stage. The output voltage of the stage 103 is developed at a point P by averaging the three input voltages together with effectively twice the reversed in sense carry-over output voltage. This is done by connecting point P through equal high resistances 135, 137 and 139 to the input terminals 113, 5 and 13 and also through a feed-back resistance 143 of half the value to the carry-over output terminal 117. The voltage at P may be applied to any suitable indicator; it is shown connected to the grid of a triode 141 controlling a neon indicator 41. Owing to the reversal of the digital representation at successive stages, the input switches 21, 29 are reversely connected to the lines 149, 155 but, to avoid this, a D.C. amplifier may be connected at the point 150 to maintain the digital representation uniform.. The input voltages may be developed by a pulse-controlled " flip-flop " triode pair (Fig. 3, not shown) with rectifiers for limiting the output voltages to the alternative values of - 17 and +23. Subtracting apparatus. The apparatus may be adapted for subtracting by reversing the input voltages for the digits to be subtracted and adding one in the lowest order. The input terminals 13, 15 and 17 (Fig. 2), for the subtracted digits are connected to additional input lines 47, 49 connected by a reversing switch 51 to the main input lines 35, 37. Additional contacts 53 of the switch connect the carry-over input 55 of the lowest order alternatively to the " 1 " and " 0 " input lines 35, 37. The apparatus therefore adds or subtracts according to the position of the switch 51.