Signal interruption system for micro-programme - inserts alternative address into micro-programme to change micro-instruction priority sequence

摘要

A sequencing circuit (1) which normally delivers sequential instruction addresses may also transfer an address applied at a special input (D) directly to its output (7). Addresses output from the sequencer determine the microprogramme steps read from a programme memory (2) and held in a register (3). A four word memory in the sequencer holds subroutine return addresses. Interrupt signals (INTE, STOP,..) are allocated priority by an interrupt priority circuit (50) which transmits the appropriate interrupt address AD and an enabling signal MIC to a multiplexor (40) which transfers selection of the next instruction from the sequencer to the interrupt circuit. Each 124 bit micro-instruction contains 10 bits which are fed back at R to initialise the sequencer to the new programme location, thus initiating the interrupt service routine, and the sequencer now resumes control till the end of the service routine is detected.