User guide

840 USE 115 00 Version 1.0
77
C
Quantum Ethernet TCP/IP
Modbus Application Protocol
C.1 Introduction
The Modbus Application Protocol
(
MBAP
)
is a la
y
er-7 protocol providin
g
peer-to-
peer communication between pro
g
rammable lo
g
ic controllers
(
PLCs
)
and other
host-based nodes on a LAN. Collectivel
y
these nodes implement all or part of a
control application used for industrial automation applications in the automotive, tire
and rubber, food and bevera
g
e, and utilities industries, to name a few.
Modbus protocol transactions are t
y
pical re
q
uest-response messa
g
e pairs.
Modbus re
q
uests contain function codes representin
g
several classes of service
includin
g
data access, online pro
g
rammin
g
, and pro
g
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
y
communication
s
y
stem that supports messa
g
in
g
services. However, the current Quantum
implementation transports Modbus Application Protocol PDUs over TCP/IP. Both
Ethernet II and IEEE 802.3 framin
g
are accommodated, althou
g
h Ethernet II
framin
g
is the default.
For more information, consult the Modbus Protocol Reference Guide
(
PI-MBUS-
300
)
.