Patent GB-734485-A (GB)
Title: Improvements in or relating to electronic digital computing devices
Inventor: KILBURN TOM
IPC: G06F7/52
Filed: 1950-04-13
Abstract: 734,485. Digital electric calculatlng-apparatus. NATIONAL RESEARCH DEVELOPMENT CORPORATION. April 3, 1951 [April 13, 1950], No. 9175/50. Class 106 (1) In a binary series-mode type electronic multiplying machine the multiplicand is repeatedly made available progressively at doubled value at each successive step of the multiplication process and, according to whether the appropriate multiplier digit is " 1 " or " 0," is passed to or withheld from the accumulator. The multiplicand is read out from the main store MS through a programme-controlled gate 16 to an auxiliary storage unit DS comprising a C.R.T. with regenerative loop 11 and, in addition to the usual amplifier, read unit and write unit, a doubling or " multiply by two " circuit 12 such as that described in Specification 734,072. Simultaneously the multiplicand is applied to a gate 19 where the presence of a " 1 " digit in the first or lowest significant position allows a coincident p-pulse to operate a trigger circuit TC1. A gate 17 is also opened to superpose a p pulse on the signal entering the storage unit DS and thus provide a " 1 " digit in the lowest significant position if it was originally absent, this being essential for carrying out the invention. Subsequently, under control of the programming unit, the multiplier is fed from the main store MS through a gate 25 to the input of a gate RG, another input of which is fed with the read output from the store DS. The occurrence of a " 1 " in the least significant place of the multiplier in coincidence with the " 1 " in the similar order of the multiplicand causes a trigger circuit TC3 to operate and open a gate 21 to permit the whole of the multiplicand to pass through to the accumulator A; if the multiplier digit is a " 0 " the circuit TC3 is not operated and the multiplicand is withheld from the accumulator. A further trigger circuit TC4 is operated by the delayed " 1 " digit of lowest significance of the multiplicand so that only one digit of the multiplier is sampled at each step. During successive steps the operation is similar but the " 1 " digit of lowest order in the multiplicand becomes progressively delayed and, by operation of the trigger circuit TC4, each successive digit of the multiplier is sampled and the input of the progressively doubled multiplicand to the accumulator controlled accordingly. The prepulses which initiate each " bar " or major machine cycle, are suppressed until the multiplication process has been completed by repeated operation of a trigger circuit TC5 controlling a gate 26 at the prepulse generator PPU. The trigger circuit TC5 is tripped by the multiplier signal passing through a gate 24, and is restored by the normal " halver " waveform available in the machine. The progressively delayed operation of the trigger circuit TC4 controlling the gate 24 prevents the lower denominations of the multiplier from passing to the trigger circuit TC5 until, when the multiplication is complete, the whole of the multiplier is blocked by the gate 24, the trigger circuit TC5 is not operated, and a prepulse passes through the gate 26 to initiate the next major machine cycle. If the trigger unit TC1 was not operated by the first digit of the multiplicand, this digit must have been " O " and the product standing in the accumulator is therefore too great by an amount equal to the multiplier. A " +1 " is now sent out by the test unit TU to the control unit CL, and this brings forward the next instruction in the programme which is arranged to cause the multiplier to be subtracted from the item standing in the accumulator. If, on the other hand, the trigger circuit TC1 was operated by a " 1 " in the lowest order of the multiplicand, it conditions the test unit TU to send " +2 " to the control unit CL at the beginning of the next cycle and thus skips the correction instruction. In a modification the gate 21 which feeds the multiplicand to the accumulator is provided with a further controlling connection which is fed with output voltages, combined in an " OR " gate, from the trigger circuits TC1 and TC4. TC4 opens gate 21 to permit all the multiplicand digits except the first to pass, while TC1, when triggered, conditions the gate 21 to pass all the digits, including the first. Specifications 645,691, 657,591, 705,474, 705,479, 712,172, 731,341, 734,075 and 734,483 also are referred to.