GB1508854A - Data handling system - Google Patents

Abstract

1508854 Data transmission INTERNATIONAL BUSINESS MACHINES CORP 4 July 1975 28183/75 Addition to 1365838 Heading H4P [Also in Division G4) A data handling system includes a number of data handling devices 3 each arranged to communicate with a common controller 1 on an interrupt basis by issuing requests for service over a common interrupt line 6 associated with a common parallel bus 2, each device having an assigned interrupt number 4 and being arranged, in response to an invitation from the controller, made in response to a detected request, to compete for service by presenting its interrupt number in parallel to a respective gating circuit 5, the gating circuits being connected to the bus and arranged to interact via the bus to place the highest priority interrupt number presented onto the bus. The arrangement applies the concept described in parent Specification, which uses a serial bus, to a parallel bus. As described any handling device 3 requiring service sets its latch 7 and applies a signal via line 6 to the central controller 1. When the controller is free it supplies an instruction via parallel bus 2 to the devices 3 in response to which each device requiring service supplies its priority number from a register 4 or from a hard wired arrangement to the corresponding gating network 5. The gating networks interact via bus 2 so that only the highest priority number is applied to the bus. After issuing the instruction the central controller waits for a period sufficient to allow the gating networks to stabilize and then services the highest priority device. The priority numbers may also form the addresses of the devices 3 which may be processors competing for a shared memory or peripherals communicating with a central processor. More than one priority order may be provided, each device 3 having two or more priority numbers, each number being associated with a respective line 6. The controller decides the priority order required and responds to the appropriate line 6 to issue an instruction to cause the appropriate priority number to be emitted. The specification describes two gating networks 5, Figs. 2 and 3 (not shown), one of which stabilizes quicker than the other.