Patent GB-869466-A (GB)
Title: Improvements relating to output converters for digital computers
Inventor: FROGGATT ROBERT JUSTIN
IPC: H03M7/00
Filed: 1956-09-15
Abstract: 869,466. Digital electric calculating-apparatus. ELECTRIC & MUSICAL INDUSTRIES Ltd. Sept. 4, 1957 [Sept. 15, 1956], No. 28266/56. Class 106 (1). Apparatus for converting a pure binary number to a binary-decimal or like scale comprises a first store for serial signals representing the binary number, a second store for equivlents in the other scale of all possible binary digits plus appropriate fillers, gating means responsive to signals from the first store to select equivalents and fillers from the second store, means for adding signals to previously converted amounts in a third store, and means for selectively subtracting the fillers in dependence on the occurrence of carries in predetermined positions in the resultant produced by the adding means. Each conversion requires one complete revolution of a magnetic drum 3, Fig. 3. which carries storage tracks 5, 4 containing respectively, binarydecimal and binary-sterling equivalents (including " fillers ") in sequence of all possible significant digits of a 36-bit word. During one revolution of the drum the word to be converted circulates 72 times in a store 1; each circulation is termed a "minor cycle." A further storage track 6 on the drum contains gating pulses for examining each binary digit in succession during the conversion cycle. The binary-decimal track 5 is selected when a terminal 25 is held at zero potential; the binary sterling track 4 is selected when the terminal 25 receives a positive potential. Negative sign detection.-During the first minor cycle of the store 1 a clock pulse from a timing device 22 is applied to a gate 30 as the 36th digit passes. This digit represents the sign of the stored number and, if it is found to be " 1 " = negative, a pulse is passed on to set a bi-stable circuit 42 which conditions a complementer 41 so that signals from the store 1 which otherwise would pass through unchanged, are complemented. The negative signal is sent also to the adder and printer 13. Lowest-order digits. Since the lowest three binary digits in the store 1 will not be affected by the conversion, a gating pulse on line 50, occurring during the passage of these digits in the second minor cycle, opens a gate 34 to allow. these signals to pass directly to the adder and printer 13. Remaining digits. During the fourth minor cycle a gating pulse from track 6 examines the fourth digit from the store 1 at a coincidence gate 35; if the digit is " 1 " a bistable circuit 37 is set. The device 37 receives a resetting pulse on a line 48 at the beginning of each minor cycle and therefore is reset at the beginning of the fifth cycle thus causing, via a differentiating device 38, the setting of a further bistable device 39 which conditions a gate 36 to allow signals from the selected one of tracks 4 or 5 to pass to the adder and printer 13. The device 39 is reset via a 72-digit delay 40. The signals derived from tracks 4 or 5 represent the value of the significant binary digit detected in the fourth position in the store 1 expressed as a binary-decimal or binary sterling number, respectively, plus a filler amount, this number consisting of twelve groups of six binary digits each. As six binary digits represent a scale of 64, the fillers will be 54 for decimal, 44 for shillings, and 52 for pence. The fifth and each successive binary digit in the store 1 is treated in a similar fashion. Accumulator arrangement.-Each amount derived from the track 4 or 5 is combined with the total in a circulating store 14, Fig. 1, by an adder 13. Since, however, each of these amounts includes fillers provision is made to deduct the filler at any stage where the adding process does not give a carry over from one decimal (or sterling) order to the next. Subtraction is performed by a device 23 which receives results, from the adder 13 through a six-binary-digit delay 15, fillers being fed to it under the control of the clock unit 22 and gates 19, 20, 21. Whenever a carry-over occurs a gate 13a passes the signal to set a bistable device 16 which inhibits a gate 18 preventing the supply of a filler for subtraction. Specification 869,465 is referred to.