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MELSEC-Q
5 FUNCTIONS
5.2 Master Function
This section explains the functions of the QJ71MT91 as a master of MODBUS
R
/TCP.
5.2.1 Automatic communication function
The automatic communication function allows device read/write request messages to
be automatically issued from the QJ71MT91 to the MODBUS
R
/TCP-compatible slave
devices.
Device memory
Auto refresh
Ethernet
Programmable
controller CPU
Buffer memory
Holding register
Holding register
100ms read
1000ms read
250ms read
QJ71MT91
(Master function)
R
R
100ms write
R
Holding register
R
MODBUS /TCP slave device
(Third party sensor, etc.)
MODBUS /TCP slave device
(Third party programmable
controller)
MODBUS /TCP slave device
(Third party remote I/O, etc.)
MODBUS device read/write request
messages are issued to the slave
repeatedly at specified intervals.
(1) To use automatic communication function
Set the automatic communication parameters to use this function.
Refer to Section 7.3 for details of the automatic communication parameters.
(2) Start and stop of automatic communication function
(a) When the automatic communication parameters are set from the utility
package (GX Configurator-MB), the automatic communication function is
activated by powering ON the programmable controller from OFF or by
resetting the programmable controller CPU (with the programmable
controller CPU's RUN/STOP switch set to RUN).
The automatic communication will not start if the programmable controller is
powered ON from OFF or if the programmable controller CPU is reset (with
the programmable controller CPU's RUN/STOP switch set to STOP).
If the QJ71MT91 is mounted on a MELSECNET/H remote I/O station, the
automatic communication function is activated when the remote I/O station
receives the information notifying the status change (from STOP to RUN) of
the remote master station's programmable controller CPU.
Setting the automatic communication parameters from GX Configurator-MB
eliminates the need of a sequence program for start.