Patent GB-775974-A (GB)
Title: Improvements in or relating to computing devices
Inventor: BOOTH ANDREW DONALD
IPC: G06F7/498
Filed: 1952-05-28
Abstract: 775,974. Digital electric calculating-apparatus; counting-apparatus. NATIONAL RESEARCH DEVELOPMENT CORPORATION. May 28, 1953 [May 28, 1952], No. 13587/52. Class 106 (1). An electrical decimal computer comprises an electro-mechanical switching device forming a pulse generator which supplies, during an initial part of an operation cycle, one to nine pulses on respective conductors, and subsequently effects sequential switching operations, an adding register comprising decimal counters each having a pulse input which may be connected by digit-value entry means to any one of the nine conductors, and separate transfer circuits between adjacent counters each including a buffer memory device whose carry-indicating output is applied to the next higher counter via an individual control circuit, the control circuits being rendered operative in turn, in order of increasing decimal significance, by successive switching operations of the electro-mechanical device, to effect a progressive carry digit propagation through the series of counters. Adding and subtracting apparatus. The apparatus shown in Fig. 1 comprises a register or accumulator A including decimal counting stages C1-C20 and carry-registering two-state buffer devices B1-B19, a keyboard KA, add/subtract switch A/S and pulse generator PA. For addition, the switch A/S is in the position shown and a number set up on KA by selectively operating key-switches k0-k9 in banks K1-K10 is entered in stages C1-C10 of the accumulator by pulses obtained from PA which, on applying a pulse over lead 11 by switch PBSA, operates through a single cycle comprising intervals t1-t30, Fig. 2. The number-entering pulses, one to nine respectively (see Fig. 2 (a)-(d)) on leads P01-P09 connected to all switches k1-k9 are applied during t1-t9 and are followed during t11-t29 by carry-controlling pulses applied in succession over pairs of leads CL1-CL19 to buffer devices B1-B19 (Fig. 2 (f)-(i), to cause " 1 " to be entered in the next counter stage C2-C20 if a buffer device has been switched to the carry state by its preceding stage C1-C19, the buffer devices being reset at t30 by a " clear " pulse (Fig. 2 (j)) over lead 10. For subtraction, the contacts AS1-AS9 of switch A/S change the connections between P01-P09 and P10-P19 so as to cause pulses corresponding to the nines complement of the number set up on KA to be entered in the accumulator, an additional " 1 " being entered in the lowest denomination through contact asc by a pulse over lead 12 at t10 (Fig. 2 (e)). The pulse generator PA may comprise a rotatable drum (Figs. 9 and 10, not shown) having conductive portions inset in a surface of insulating material, these portions being engaged by stationary resilient Contact members from which the pulse outputs are obtained. The drum is driven by a continuously operating motor through a one-revolution clutch operated by an electromagnet which receives the pulse on lead 11. Accumulator. Fig. 6 shows two stages C, C2 of the accumulator A, Fig. 1, each comprising a multi-cathode discharge tube having a central anode 30 surrounded by ten separate cathodes 31<SP>0</SP>-31<SP>9</SP> and first and second guide electrodes 32<SP>0</SP>-32<SP>9</SP> and 33<SP>0</SP>-33<SP>9</SP>. A discharge normally takes place between only one of the cathodes and the anode, and the position of this discharge can be viewed against a scale on the end of the tube. A negative input pulse at 60 or 61 will be applied directly to the first guide electrodes and through an R.C. delay circuit 35, 34 to the second guide electrodes, thus shifting the discharge to the next cathode in clockwise direction. When the discharge shifts from 31<SP>9</SP> to 31‹ a positive carry pulse will be applied to output terminal 62, and to the associated buffer device such as B1 which, as shown, comprises a thyratron 37 which is fired by this pulse and remains conducting to register the carry until the negative " clear " pulse is applied over lead 10 to its anode. Thus, when PA completes a circuit over leads such as CL1, if a carry is registered a negative pulse will be applied to terminal 64 and to input terminal 61 of the next counting stage such as C2. In the alternative shown in Fig. 7, a counting stage comprises a disc 45 of ferro-magnetic material having ten teeth 47<SP>0</SP>-47<SP>9</SP>, one of which is normally held opposite an electromagnet 48 energized from a D.C. source +V. An input pulse causes successive energization of electromagnets 49, 50, which are so spaced relatively to the teeth as to cause the disc to rotate clockwise by one tooth, magnet 48 having a second winding whereby its effect is decreased while magnet 50 is energized. Alternatively, 48 may be a permanent magnet of less strength than electromagnets 49, 50 when energized. A carry pulse is obtained by a roller 123 on the disc closing contact blades 120, 121. Multiplication and division. Fig. 3 shows an arrangement for effecting multiplication and division by repeated addition and subtraction respectively, including the apparatus of Fig. 1, and ganged 10-position selector switches U1-U13 stepped by pulses applied to a motor SM. For multiplication, the multiplicand is set up on the keyboard KA, and the multiplier on the ten-bank keyboard KM associated with a pulse generator PM, switch M/D2 being closed and M/D1 open. During a cycle of operations, in response to a control input pulse, PM produces one to nine pulses respectively on leads PM01-PM09 during time intervals tm1- tm9 (Fig. 4, not shown), each long enough for a complete cycle of PA, and produces a final pulse on lead 13 which is applied to SM. This latter pulse is also sent through U12 (except when it is in the initial position shown) and M/D2 to the input lead 14 of PM. Thus, once PM receives an initiating pulse it passes through ten cycles during each of which a number of pulses corresponding to one of the multiplier digits is applied through U11 to PA to cause the latter to pass through a corresponding number of cycles during each of which the multiplicand is added in denominations of the accumulator A selected by U1-U10. At the same time, the multiplier is entered in a register B comprising counting stages Cm1- Cm10 connected to the output of U11 through U13. For division, the dividend is first set up on keyboard KA and entered into the accumulator A; the divisor is then set up on KA and switches M/D1, M/D2 operated to the position shown to select a pulse generator PD, instead of PM, for repeated cyclic operation. This generator produces during each cycle, in response to a control input pulse on lead 16, ten pulses on lead 18 followed by one pulse on lead 19 and a final switch-stepping pulse on lead 20. The switches U1-U10 and U13 perform denominational shifting as in multiplication, a further switch UX controlling the entry of nines in the accumulator during subtraction. A trigger circuit BC, e.g. of the Eccles-Jordan type, associated with the highest denomination counting stage C20, controls an electromagnet SO for operating switch A/S. and a relay G in such a manner that, at the beginning of each cycle of PD, pulses on lead 18 are passed through contact g1 to PA and each cause a subtractive entry of the divisor into the accumulator, and are also passed through U13 to the appropriate stage of register B to count the number of such entries; when however, the number in the accumulator goes negative (" 9 " registered on C20 instead of "0"), BC changes state, thereby switching over A/S to the add position, opening contact g1 and closing g2. The subsequent pulse on 19 causes a correction cycle of PA in which the divisor is added in the accumulator and " 1 " is subtracted from the operative stage of B by applying thereto the nine pulses on P19. Thus, after the ten cycles of PD have been completed, register B and accumulator A contain the quotient and remainder respectively.