Interface between a system control unit and a service processing unit of

Abstract

A computer system includes a plurality of central processing units (CPUs), a main memory, a system control unit (SCU) for controlling the transfer of data between the CPUs and the main memory, and a service processing unit (SPU) to interface the computer system with the outside world, such as an operator console. The method used for interfacing the SPU and SCU includes delivering a BUFFER FULL handshaking signal from the SPU to the SCU in response to the SPU receive buffer having data contained therein and being unavailable to receive data. The SCU responds to the absence of the BUFFER FULL handshaking signal by delivering a TRANSMIT FRAME handshaking signal to the SCU. A preselected duration of time after delivering the transmit frame, the SCU delivers the actual data in a series of fourteen consecutive clock cycles. Further, the method for delivering data from the transmit buffer of the SPU to a receive buffer of the SCU includes delivering a BUFFER REQUEST handshaking signal from the SPU to the SCU in order to determine if a buffer is currently available in the SCU. When a receive buffer grant becomes available in the SCU, a buffer grant handshaking signal is delivered to the SPU. The SPU responds by delivering the actual data in fourteen consecutive clock cycles.