Modbus/TCP is a variant of the Modbus family of simple, vendor-neutral communication protocols intended for supervision and control of automation equipment. Specifically, it covers the use of Modbus messaging in an intranet or Internet environment using the TCP/IP protocols. The most common use of the protocols at this time is for Ethernet attachment of PLCs, I/O modules, and "gateways" to other simple field buses or I/O networks.
Every device is identified by its unique address. Its registers are read as Input (1 bit long) or Input Register (16 bits), or written to as Coil (1 bit) or Holding Register (16 bits). Registers of each type are addressed by using 16-bit numbers.
See Also:
Introduction to Modbus OPC Server