Stealth interface for process control computers

A stealth interface for providing transparent data transfers between an actively redundant process control computer and at least one front end computer which is capable of communicating with a computer network, said interface comprising:

• a multi-ported data memory having an internal port connected to a bus structure of said process control computer and at least one external port for communicating with said front end computer, said multi-ported data memory having a variable section for periodically storing data collected by said process control computer, and a mailbox section for storing messages from said front end computer to said process control computer;
• external access control means, coupled to a clock signal associated with operation of said process control computer, for enabling at least one word address in said multi-ported data memory to be accessed from said external port only during a predetermined portion of a cycle for said clock signal;
• and
• guardian means connected to said multi-ported data memory for limiting write access permitted from said external port to predetermined address locations in said multi-ported memory.

A stealth interface for providing transparent data transfers between an actively redundant process control computer and at least one front end computer which is capable of communicating with a computer network, said interface comprising:

• a multi-ported data memory having:
• at least one internal port for communicating with said process control computer;
• at least one external port for communicating with said front end computer;
• a variable section for periodically storing data collected by said process control computer;
• and
• a mailbox section for storing messages from said front end computer to said process control computer;
• and
• access control means for enabling said multi-ported memory to be addressed from said external port only during a predetermined portion of an operative clock cycle for said process control computer, so that either at least one data word stored in memory in said variable section of said multi-ported memory may be transferred to a memory associated with said front end computer or at least one message word may be transferred from said front end computer to said mailbox section of said multi-ported memory without any interference with the operation of said process control computer.