Patent GB-981616-A (GB)
Title: A data transfer device
IPC: G06F3/14
Filed: 1961-06-23
Abstract: 981, 616. Plugboard controlled computors; data transfers. INTERNATIONAL BUSINESS MACHINES CORPORATION. June 23, 1961 [July 5, 1960], No. 22779/61. Heading G4A. A serial computor, that described in Specification 981,615, has a basic data transfer cycle in which a character taken from a first variable length field of a magnetic core store is read into a buffer store whence it is regenerated in the first field and also read into an arithmetic unit, after which a character taken from a second variable length field is read out to the buffer, combined with the character from the first field or otherwise processed in the arithmetic unit, after which the result is written into the second field. Scanning, i.e. timing of reading and writing, of the first field is under the control of a chain 9 of triggers, and of the second field is under the control of a chain 10. The present invention is concerned with modification of the basic transfer cycle to perform operations the necessity for which may not be apparent until a field has been scanned. Such operations are complementing the result of a subtraction, indicated by a carry from the highest order location of the second field, or elimination of non-significant zeros before printing in which the significance of a zero is determined by the presence of a higher order non-zero digit. These operations all involve coincidence of the first and second fields (single field operation). Basic cycle. A digit time in which one order from each field is processed consists of two bit times during each of which an I pulse followed by an A pulse issues from timer 7a. An A pulse when gated through and circuit 26 by trigger 21 being on generates a signal S which steps scanner 9 one position, and when gated through and circuit 23 generates a signal s which steps scanner 10. When the two fields are not the same field a signal 2Ad is present at or circuits 25, 28 with the result that signal S passes gate 27 to switch trigger 21 off and signal s passes gate 24 to switch trigger 21 on. It follows that memory scanning is under the control of scanner 9 for one bit time after which it is stepped and control is transferred to scanner 10 for the next bit time. One address operation occurs when the first and second fields coincide. During this operation scanning may be under the control of only one of the scanners for several digit times. Scanning by scanner 9 occurs when trigger 22 is off and by scanner 10 when trigger 22 is on. Comblementing is initiated by and circuit 32 being up due to imput signals C 2 , set and N which indicate respectively that complementing is to be performed, that the scanners are ready to scan the field and that the field does contain numerical as distinct from alphabetic or special characters. And circuit 35 is enabled and switches trigger 22 off. Scanner 9 then operates (trigger 21 is on and gate 27 is closed with the result that S signals cannot switch trigger 21) until the detection of a mark added to a numerical character to indicate end of field to be complemented causes a signal L to issue, enables and circuit 38 and switches trigger 22 on. Scanner 10 then operates. Each character is sent to arithmetic and returned to memory after being complemented. Sensing of the mark again causes signal L to issue and scanner 9 again takes over unless trigger 42 is switched to indicate end of numerical zone and and circuit 32 goes down. Suppression of non significant zeros is initiated by a signal i 2  applied to and circuit 33. The number to be examined has been placed in a particular section of memory from which data is read to a printer and it is assumed consists of several groups of numeric characters separated by "blank" characters which indicate the spacing of the groups on the printed sheet. A signal # from buffer 5 indicates that the numeric character just read out is non-zero, a signal # that the character is a blank. Scanner 9 begins the scan of the field and if examination of a character leads to a signal # control is switched to scanner 10 in the next bit time whereupon the character is read out and printed. If signal # does not issue scanner 9 continues to control read out and examination of the characters. If a signal # issues a result of this further scanning, scanner 10 again takes control and prints the zeros as zeros. If a signal # issues this again switches control to scanner 10 but additionally causes the control unit 8 (details not shown) to replace the zeros as blanks in the printer. Modifications are possible to cause non-significant zeros to be replaced by a special character such as an asterisk, to enter a cash sign to the left of the highest significant digit and to differentiate between zeros to the left or right of a decimal point.