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1.1 Features
1
OVERVIEW
(2) Supporting the slave function of MODBUS communication
The QJ71MB91 supports the slave function of the MODBUS communication, which
is an open network system for factory automation, and thereby is compatible with
various MODBUS master devices (hereinafter referred to as master) of other
manufacturers.
The slave function includes the following two functions.
(a) Automatic response function
The QJ71MB91 can automatically respond to a request message received from
the master.
Any sequence program for the slave function is not needed.
(b) MODBUS device assignment function
Using MODBUS device assignment parameters, the MODBUS devices are
correlated with the programmable controller CPU device memory.
This enables direct access from the master to the programmable controller CPU
device memory.
Supporting the MODBUS devices of large capacity, the QJ71MB91 allows all
device memories of the programmable controller CPU to be assigned.
Figure 1.3 MODBUS device assignment function
D300
D299
Device
400499
D300
400500
D301
400501
Device
1234H
R
R
R
Programmable
controller CPU
No sequence
program required
MODBUS device assignment parameter
QJ71MB91 (Slave function)
MODBUS device
RS-232, RS-422 or RS-485
Request message (Write 1234
H
to holding register 400500)
MODBUS
Master
device
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