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1.1 Features
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OVERVIEW
CHAPTER1 OVERVIEW
This manual explains the specifications, functions, programming, and troubleshooting of
the MELSEC-Q series QJ71MB91 MODBUS interface module (hereinafter referred to
as QJ71MB91).
The QJ71MB91 is used when a MELSEC-Q series programmable controller is connected
to the MODBUS protocol system.
MODBUS is a registered trademark of Schneider Electric S.A.
1.1 Features
(1) Supporting the master function of MODBUS communication
The QJ71MB91 supports the master function of the MODBUS communication,
which is an open network system for factory automation, and thereby is compatible
with various MODBUS slave devices (hereinafter referred to as slave) of other
manufacturers.
The master function includes the following two functions.
(a) Automatic communication function
By setting the automatic communication parameters, MODBUS device data can
be automatically read from or written to the slaves at the specified intervals using
the QJ71MB91 buffer memory.
*1
Data can be transferred between the QJ71MB91 buffer memory and
programmable controller CPU device memory by making the auto refresh setting
with the utility package (GX Configurator-MB) or by accessing any intelligent
function module device with a sequence program.
* 1 The MODBUS
device is defined as a device area of the slave where data can be read/written in
response to a request from the master.
Figure 1.1 Communication using the automatic communication function
R
MODBUS slave device
(Third party sensor, etc)
R
MODBUS slave device
(Third party programmable
controller)
Device memory
R
MODBUS slave device
(Third party remote I/O, etc)
Holding register
Holding register
Holding register
4
2
5
3
1
6
7
(FG)
(FG)
RS-232
/485
RS-422
CH2
RDB
RDA
SDB
SG
SDA
CH1
QJ71MB91
RUN
RD
NEU.
SD
NEU.
RD
SD
CH1
CH2
ERR.
RS-485
Programmable controller CPU
Device memory
Auto Refresh
QJ71MB91 (Master function)
Read
Read
Read
Write
Buffer memory
Automatically issues the
MODBUS device read/write
request message to Slave.
R
Summary of Contents for QJ71MB91
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