Apparatus for interfacing a real-time communication link to an

Abstract

An interface between a real-time data link and a digital computer system utilizes data buffers between the computer central data storage and the data link. An interface control processor is responsive to a Data Transfer Command set comprising a SEND, a GET, a SET-TAG and a TERMINATE command. The commands include a TAG parameter that is set by the SET-TAG command to group sequences of SEND and GET commands so that logical streams of data are continuously transmitted and received across the interface. The SEND command includes a RECEIVE parameter to initiate the transfer of received data from the data link to the buffers after all data associated with the SEND command has been transmitted. Data transmission and reception operations are terminated by a TERMINATE command with a TAG parameter matching the TAG parameters of the sequence of commands controlling the operations. The SEND, GET and SET-TAG commands are stacked in a command queue and applied sequentially to the control processor. The TERMINATE command bypasses the command queue and is applied directly to the control processor for terminating operations associated with a sequence of commands with matching TAG parameters. In response to SEND, data is transferred from central data storage to the buffers for transmission to the data link. In response to GET, received data is transferred from the buffers to the central data storage. A buffering strategy maintains the buffer as full as possible during data transmission and as empty as possible during data reception.