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Appendix
A. What is Modbus TCP/IP?
Modbus is a communication protocol that was developed by Modicon Inc. in 1979, and was
originally designed for use with Modicon controllers.
Detailed information regarding the Modbus protocol can be found at: http://www.modbus.org.
The different versions of the Modbus protocol used today include Modbus RTU, which is based on
serial communication interfaces such as RS-485 and RS-232, Modbus ASCII and Modbus TCP, which
uses the Modbus RTU protocol embedded into TCP packets. Modbus TCP is an internet protocol.
The protocol embeds a Modbus frame into a TCP frame so that a connection oriented approach is
obtained, thereby making it more reliable.
The master queries the slave and the slave responds with a reply. The protocol is open and, hence,
highly scalable.
PET-AR400 User Manual
V1.0.0
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