5
FUNCTIONS
5.2 Master Function
5.2.2 Communication by dedicated instructions
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5.2.2 Communication by dedicated instructions
The dedicated instructions allow reading/writing of MODBUS devices at any timing with a
sequence program.
The following is a list of available dedicated instructions.
Figure 5.11 Communication by dedicated instruction
Table5.4 Dedicated instruction list
Dedicated
instruction
Description
Reference
MBRW
Issues a MODBUS
device read/write request message to a slave.
MBREQ
With this instruction, a request message can be sent to a slave in any
given Protocol Data Unit format.
[Z.MBRW ]
Command
400500
MODBUS slave device
Holding register
1234
H
R
Programmable
controller CPU
Device memory
1234
H
QJ71MB91
(Master function)
Request message (Read request for holding register 400500)
Response message (Holding register 400500 = 1234
H
)
RS-232, RS-422 or RS-485
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