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MELSEC-Q
1 OVERVIEW
(b) Communication using dedicated instruction
Dedicated instructions can be used to make communication from a
sequence program at any timing.
The QJ71MT91 supports the following two dedicated instructions.
1) MBRW instruction
Reads/writes MODBUS
R
device data from/to a slave.
This enables slave data to be read out to the programmable controller
CPU device memory or programmable controller CPU data to be
written to the slave.
2) MBREQ instruction
Can issue user-desired request message format (function code 1 +
data unit) to a slave.
1: Refer to Chapter 4 for the function code.
[Z.MBRW ]
Command
MODBUS /TCP slave device
Holding register
Programmable
controller CPU
QJ71MT91
Device memory
1234
H
1234
H
Request message (holding register 400500 read request)
400500
Response message (holding register 400500 = 1234H)
(Master function)
Ethernet
R
1
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