Protocol for Signaling the Use of an Optional Feature by a Channel and Control Unit
Original Publication Date: 1986-Jun-01
Included in the Prior Art Database: 2005-Mar-09
During initial selection of an I/O device, a channel and a control unit use a new protocol to signal the availability of an optional feature for a data transfer. The protocol can be used with various optional features or with a set of optional features. To signal the use of the optional feature, the control unit raises Mark 0 In when it raises Address In, and it drops Mark 0 In when it raises Status In. (Address In, Status In, Mark 0 In, and the other signals control a data transfer, the initial selection of a device preceding the data transfer, and subsequent ending operations. The use of Address In, followed by Status In is part of the sequence of signals that a control unit sends to the channel during initial selection. Mark 0 In is used by the control unit during a data transfer but not during initial selection.