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77
C
Quantum Ethernet TCP/IP
Modbus Application Protocol
C.1 Introduction
The Modbus Application Protocol
MBAP
is a la
er-7 protocol providin
peer-to-
peer communication between pro
rammable lo
ic controllers
PLCs
and other
host-based nodes on a LAN. Collectivel
these nodes implement all or part of a
control application used for industrial automation applications in the automotive, tire
and rubber, food and bevera
e, and utilities industries, to name a few.
Modbus protocol transactions are t
pical re
uest-response messa
e pairs.
Modbus re
uests contain function codes representin
several classes of service
includin
data access, online pro
rammin
, and pro
ram 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 an
communication
s
stem that supports messa
in
services. However, the current Quantum
implementation transports Modbus Application Protocol PDUs over TCP/IP. Both
Ethernet II and IEEE 802.3 framin
are accommodated, althou
h Ethernet II
framin
is the default.
For more information, consult the Modbus Protocol Reference Guide
PI-MBUS-
300
.
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