Abstract: A control system allows for transferring messages between a programmable logic controller and a host computer over a serial data communications network. The programmable logic controller executes a ladder program and has an integral network interface module for permitting direct communicative coupling to the communications network. Messages can be received and sent by the programmable logic controller without interruption of the execution of the ladder program. The programmable logic controller can receive unsolicited messages from the host computer.

Abstract: "A Manufacturing Automation Protocol (MAP) interface unit couples a local area network (LAN) to a MAP network. The LAN includes a plurality of industrial programmable logic controllers (PLCs) and the MAP network includes a plurality of MAP devices. The MAP interface unit comprises a CPU for performing a plurality of routines. A first routine controls the coupling of the MAP interface unit to the MAP network and a second routine controls the coupling of the MAP interface unit to the LAN. A further routine disposed between the first coupling routine and the second coupling routine converts messages from the MAP devices on the MAP network to messages to the PLCs on the LAN and converts messages from the PLCs to messages to the MAP devices. These messages are either requests for data or responses with data to these requests.