Abstract: A data processing system with improved input/output (I/O) techniques is disclosed. The input/output control logic, or channel, of a central processing unit is connected to a plurality of peripheral input/output device control units, in parallel, by a plural line interface bus which includes bidirectional data transfer lines and bidirectional address transfer wires. The interface bus also includes unidirectional lines to and from peripheral device control units which synchronize operation of use of the bus. Several forms of I/O communications are shown to be controlled by the interface bus and include, direct processor controlled data transfer with simultaneous transmission of data and commands to peripheral devices, cycle steal data transfers permitting concurrent input/output operations and central processor program instruction execution, and peripheral device initiated interrupt requests to the central processor.

Abstract: The interface between I/O control logic, or channel, and peripheral devices permits simultaneous transfer of command, device address, and data, and includes logic in a peripheral device control unit for dynamic change of the attached peripheral device interrupt priority level while the device may be executing a prior command. The I/O control logic includes means for initiating serial poll signalling while other transfers are taking place on the interface.

Abstract: Common logic in a peripheral device control unit responds to a serially propagated poll signal from I/O control logic, or channel, along with a coded signal identifying either a poll for a cycle steal request or a poll for an interrupt request having one of several priorities. The poll signal received will be captured or propagated to following control units dependent upon whether the control unit has requested a cycle steal transfer, or has requested an interrupt at the priority level indicated by the coded signal accompanying the poll signal. Proper functioning of poll capture or propagation is possible even though one of the control units is physically removed from the serial chain of control units.