Modbus TCP
From SCADApedia
Modbus is a popular protocol used in control systems in many industrial sectors. Originally Modbus was used exclusively for serial communications. With the introduction of Ethernet interface cards in PLC's and other controllers, Modbus was slightly modified to operate as protocol encapsulated in TCP packets, and this modification is called Modbus TCP.
The minor Modbus modifications include removal of the CRC and the addition of a 7-byte Modbus Application Protocol header as shown in the figure below.
The protocol ID for Modbus is two bytes, both with a value of 0. The purpose of the address field at the end of the MBAP is to allow Modbus gateways to convert a Modbus TCP packet to a serial Modbus packet.
External Links
Modbus-IDA Organization Home Page
