MESSAGING APPLICATION LAYER (MODBUS) OVER ETHERNET TO TRANSPORT LAYER (TCP) COMMUNICATIONS METHOD AND APPARATUS

摘要

A communications adapter (10) is provided for interfacing between a master device (12) and an I/O device (14) (body) having an output and/or an input. In the case of the I/O body (14) having an output, the adapter has a TCP port for coupling to the master device via a trasmission path for receiving a request message. The adapter (10) also has a connector for operable coupling to the I/O device (14) for receiving the output of the I/O device. The adapter (10) further has an interface circuit operably connected to the TCP port and the connector for transmitting a response message over the transmission path in response to the request message, the response message correlating to the output received from the I/O device. The request message and the response message is limited to a length that is less than a TCP transaction length and/or a maximum transmission unit limit, or both, depending on the embodiment of the present invention.