Quantum Ethernet TCP/IP Modbus Application Protocol
C.1 Introduction
The Modbus Application Protocol (MBAP) is a layer-7 protocol providing peer-to- peer communication between programmable logic controllers (PLCs) and other host-based nodes on a LAN. Collectively these nodes implement all or part of a control application used for industrial automation applications in the automotive, tire and rubber, food and beverage, and utilities industries, to name a few.
Modbus protocol transactions are typical request-response message pairs. Modbus requests contain function codes representing several classes of service including data access, online programming, and program download and upload classes. Modbus responses can be ACKs with and without data, or NACKs with error information.
The Modbus Application Protocol can be transmitted over any communication system that supports messaging services. However, the current Quantum implementation transports Modbus Application Protocol PDUs over TCP/IP. Both Ethernet II and IEEE 802.3 framing are accommodated, although Ethernet II framing is the default.
For more information, consult the Modbus Protocol Reference Guide (PI-MBUS- 300).
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