BUS INTERFACE CONTROL CIRCUIT

摘要

A control circuit for the interface circuit of a module of a distributed process control system permits its kernel submodule and peripheral submodule to communicate through the interface circuit notwithstanding that the structure and protocol of module BUS of the kernel submodules is incompatible with the structure and protocol of the PCI BUS of the peripheral submodule. The control circuit includes a module BUS state machine (MBSM), a PCI target state machine (PTSM), an arbiter state machine (ARSM), and an address decode logic (ADL) circuit. In response to control signals from the kernel and peripheral submodules applied to the control circuit over their respective buses, and control signals produced by the MBSM, the PTSM, the ARSM, and the ADL circuit. Which one of the two submodules is granted access to the registers of the interface circuit is determined by the control circuit which also grants the peripheral submodule access through the interface circuit to the memory of the kernel submodule. If both submodules request access to the interface circuit at the same time the peripheral submodule has priority. The control circuit prevents either submodule from successive accesses to the interface circuit if the other submodule has a request for access pending.