Schneider Optics Web Embedded Server - Manual (Page 87)

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C
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).