GB1521737A - Data processing - Google Patents

Abstract

1521737 Data processing FUJITSU Ltd 28 Aug 1975 [29 Aug 1974] 35618/75 Heading G4A The processing section of a central processing unit 1 (Fig. 1) operates on instructions from either its own control memory 15 or from an auxiliary processing unit 6. As described either control memory 15 may be accessed under the control of address register 16 to cause read out to register 17 of a microinstruction to be executed by control circuit 18 connected to processing section 19, data channel 3 and main memory 2, or a signal from coupling device 14 of the auxiliary unit 6 to control unit 18 results in gate 21 being enabled to permit instructions from memory 8, light pen 10, keyboard 11 or input/output unit 13 to be entered into the register 17. At each access of control memory 15, four instructions are read out, one of these being selected in accordance with the contents of two bits of the address register 16. The register 17 has upper and lower halves each storing a microinstruction and operated alternatively. The arrangement obviates the necessity of storing in control memory 15 microprograms not in frequent use, e.g. those controlling the display of the auxiliary unit 6.