Patent GB-801538-A (GB)
Title: Reversible electronic accumulator
IPC: G06F7/498
Filed: 1957-04-08
Abstract: 801,538. Digital electric calculating-apparatus. NATIONAL CASH REGISTER CO. April 8, 1957 [April 13, 1956], No. 11367/57. Class 106 (1). An electronic accumulator with a plurality of denominational orders each operable in an additive or subtractive manner has a common switching member adapted to control the setting of an input device for each order for introducing additive and subtractive entries in the accumulator, additive and subtractive transfer devices associated one with each order, except the highest order, a further additive and subtractive transfer device associated with the highest order for producing carry signals when the capacity of the highest order is exceeded, a " fugitive one " transfer device associated with the lowest order and a control circuit responsive to carry signals from the said further transfer device associated with the highest order and adapted to control the transfer of carry signals from the highest order to the lowest order whereby a carry signal is applied to the " fugitive one " transfer device from the highest order only when the sign of the total in the accumulator changes. As described for a decimal accumulator entries are made on lines 36, 37, 38 respectively, Fig. 1, into the units, tens and hundreds orders 11, 19, 21 from a keyboard controlled impulse generator. Each order comprises a ring of gas discharge digit tubes 100, 101, 102 ... , &c., Fig. 2A. When a tube such as the " 1 "-digit tube 101 is conducting, the " 0 "-digit tube 100 is primed by its auxiliary grid 165 via the lead 167 and the " 2 "-digit tube 102 is primed by its control grid 169 via the lead 171 due to conduction in the tube 101 raising the potential at the point 175 so that an " add one " pulse on the line 152 or a " subtract one " pulse on the line 179 will cause the appropriate tube to fire. The " add " and " subtract " pulses are formed by the double triode 201 triggered by input pulses on the line 224 supplied from a keyboard controlled impulse generator under the control of an add/ subtract switch 216 shown in the " add " position. Negative numbers are represented as nines complements. Passage in the units or tens order from 9 to 0 actuates the positive side 13, Fig. 1, of transfer control means which comprises monostable double triode circuits to actuate the positive side 18 of transfer effecting means also comprising monostable double triode circuits which send an " add one " impulse to the next higher order. Reverse passage from 0 to 9 directly causes one to be subtracted in the next higher order via the negative parts 16, 20 of the transfer circuits. When the sign of the number in the accumulator changes, a " fugitive one " correction is required in the units order which is supplied by round carry from the hundreds order, an additive " fugitive one " when the sign changes from negative to positive, and a subtractive " fugitive one" when the sign changes from positive to negative. The carry pulses are supplied through bi-stable flip-flops 31, 32 which trigger the transfer effecting means 24, 25 which comprise monostable double triode circuits to pass the appropriate carry signal to the units order. These carry signals are passed under the control of a main memory 35 comprising a bi-stable double triode circuit of which section A is operative when the sign of the number in the accumulator is negative and additive " fugitive ones " only are passed and section B is operative when the sign of the number in the accumulator is positive and subtractive " fugitive ones " only are passed. Section A also operates an indicator 42 to indicate negative numbers. The action of the memory 35 ensures that carry is inhibited when the accumulator capacity is exceeded. Additional circuitry, Fig. 3, enables computations which temporarily exceed the accumulator capacity to be correctly performed. Points 66, 67, Fig. 1, are connected to leads 64, 65 respectively. In addition to the main memory 35, there is an auxiliary memory 61 of similar components, the two parts of which, N and E, correspond to " normal " and " exceed " conditions in the accumulator. In operation, when a subtractive carry is incident on line 65 and indicative of a change from " normal " to " exceed " conditions in the negative sense, the part A of memory 35 will be conducting, and a relay R5 being therefore operated the carry passes over the normally open contacts R5a1 to change the condition of the memory 61 from N to E, thereupon actuating the relay R6 and connecting an " exceed " indicator 70 to positive potential over contacts R6a3. Contacts R6b1 open so that when the accumulator capacity is subsequently re-entered, the memory 35 remains in the " A " condition. When the capacity of the accumulator is re-entered, for example, from a negative " exceed " condition, a carry signal incident on line 64 passes over contacts R6a2 and R5a2 to switch the memory 61 to N thereby de-energizing the relay R6 and hence also the "exceed" " indicator 70 and closing contacts R6b1, R6b2 so that the memory 35 is again under the control of " fugitive one " signals. The carry signal passes over the lead 87 to the transfer effecting means but is inhibited from causing a positive carry entry from the positive part thereof since with the accumulator in the " exceed " condition, relay contacts R6b5 are open and no operating potential is supplied to the transfer means 24. A detailed circuit (Figs. 2A-2F, only Fig. 2A is shown) is described wherein resetting is effected by interrupting the biasing circuit for the control and screen electrodes of the " 0 "-digit tetrode register tubes to permit conduction therein, and thereby extinguish the other tubes. An initial amount may be preset into the accumulator by rotary switches (not shown). Specification 601,146 is referred to.