Patent GB-1064518-A (GB)
Title: Electronic four-rule arithmetic unit
IPC: G06F7/57
Filed: 1964-06-24
Abstract: 1,064,518. Electronic calculating apparatus. TELEFUNKEN PATENTVERWERTUNGS G.m.b.H. June 24, 1964 [June 28. 1963], No. 26093/64. Heading G4A. An electronic calculating apparatus for the four rules comprises four registers capable of storing numbers a, b, c, d and is effective to d calculate (a  b)-, but operands are entered c in two of the registers only so that addition, subtraction, multiplication or division of these two operands is effected according to which two of the four registers are used for the operands. The arrangement described, Fig. 1, comprises four 3-word registers A-D, serial outputs from registers C, D being fed to an adder-subtracter 3 whose output is applied to register D; serial outputs from registers A, B being fed to an adder-subtracter 4 whose output is applied to register A. For the word length of 16 digits employed, as described, the registers A-D are of 48-digit length and the apparatus is controlled by a circuit 11 comprising a clock pulse generator 12 and a cycle counter 13 which produces an output every 49th pulse, this pulse period being employed to shift the contents of registers C, B one place to the right, the calculation operation being terminated after 32 such shifts, as counted by a counter 10, the result being found in the hatched portion of register A. The operands are entered initially from a keyboard 1 and the result can be printed out at 22. The numbers can be represented in the calculation in pure binary form with serial operation, or in binarycoded decimal form with serial-parallel operation. The registers may be realized by means of rotating storage devices having read and write heads.  Addition.-The numbers a, b to be added are entered in the hatched regions of registers A, B, registers C, D being set up each to contain all zeros except for a " 1 " to mark the units position of the numbers in the corresponding registers B, A. The numbers in the registers A, B together with the point representations in the registers D, C constitute effectively a " floating point " number representation. A control flip-flop 9 is arranged initially to cause addersubtracter 3 to subtract and adder-subtracter 4 to add. The adder-subtracters 3, 4 always operate in step with each other and with switch 18 in the position shown always effect opposite calculations. In operation, during the first cycle, the subtraction d-c in adder-subtracter causes a sign change in register D which is detected in the highest stage of the register thereby causing flip-flop 9 to change over so that register D is " reset " during the next cycle. A pulse on line 8 now causes the contents of registers C, B to shift one place to the right. The steps of subtraction d-c, reset, and shift continue until the " 1 "s in registers C, D are aligned. The next subtraction does not result in a sign change in register D so that there is no reset. Consequently the sum a + b is retained in register A, the subsequent calculating steps, resets and shifts merely effecting shift of the registers C, B, the required sum remaining in the hatched portion of register A. Subtraction.-This is generally similar to addition, except that switch 18 is changed over, so that in each cycle the adder-subtracters 3, 4 both add or both subtract. At the conclusion of the operation, the difference a-b is found in the hatched portion of register A. Multiplication.-The multiplicand b is set up in the register B, with its point position fixed as above by a " 1 " in register C. The multiplier is entered in the hatched region of register D, the register A being filled with zeros. The switch 18 is in the addition position, and the steps subtraction d-c (simultaneously with addition a + b), reset and shift of registers C, B take place with no significant result until the " 1 " in register C is aligned with the highest order multiplier digit in register D. Subtractions d-c occur in this position (together with corresponding addition a + b) until the multiplier digit is reduced to zero. Registers C, B are then shifted and the next lower multiplier digit in register D. The process continues until all the multiplier digits have been reduced to zero, the product (result) being found in the hatched region of register A. Division.-The dividend is entered in the hatched region of register D, register A being filled with zeros. The diviser is set up in the hatched region of register C, its units position being marked by a " 1 " in the corresponding position of register B. Subtractions d-c, resets and shifts take place as in addition and multiplication until the content of register C becomes smaller than that of register D. The result is now built up digit-by-digit in register A, the remainder being in register D at the conclusion of the division process. Modifications.-To reduce the calculating time, unnecessary subtractions and resets are obviated by providing means to compare the contents of the registers C, D before a subtraction takes place (Fig. 3, not shown). The registers can be combined to form two doublelength registers A-D and B-C with one third of each register being omitted at the joint; negative numbers can be represented in complement form, the whole register B-C being complemented when a change of sign takes place in register D (Fig. 4, not shown).