GB1441661A - Data processing system - Google Patents

Abstract

1441661 Data processing system INTERNATIONAL BUSINESS MACHINES CORP 30 Aug 1973 [29 Sept 1972] 40775/73 Heading G4A A data processing system includes a store containing a number of sequence control words each including two address fields, the first of which accesses a corresponding stored program routine and the second of which accesses a further sequence control word, and means, responsive to interrupt signals, to access a further sequence control word in response to the second address field unchanged when no interrupt signals are active and in reponse to a predetermined logical combination of the second address field and the interrupt signals when one or more of the interrupt signals are active. Each sequence control word contains a field (the left hand field in Fig. 1) by means of which a corrresponding microprogram routine is accessed. The right hand field contains an address, in the form of two four bit hexadecimal characters, which is used to access the next control word. Four interrupt leads are provided giving sixteen combinations and the interrupt signals are OR-ed with bits of the right hand address character. The resulting address is used to access the next control word by doubling and adding one, the address of each control word being shown above the corresponding word in Fig. 1. The arrangement may be used in time sharing systems where each machine cycle is divided, in this case, into sixteen, the particular sequence of control words depending on the state of the interrupt signals. The programs selected by the control words may relate to I/O devices sharing a common program store. The interrupt signals may be generated within the system or externally, e.g. by I/O devices requiring service.