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7
PARAMETER SETTING
7.4.4 MODBUS extended file register assignment
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(1) MODBUS extended file register assignment
The MODBUS extended file register assignment to the programmable controller
CPU is fixed to the file register (ZR).
The MODBUS extended file register is assigned to the file register (ZR) of the
programmable controller CPU as shown below.
(2) Out-of-bounds read/write request
The QJ71MT91 sends an exception response when the master makes a request
to the programmable controller CPU on the QJ71MT91-mounted station to read
from or write to a nonexistent file register (ZR).
For the file register (ZR), refer to the QCPU user's manual (explanation, program
fundamentals).
(3) MODBUS extended file register size
The MODBUS extended file register size depends on the file register (ZR) size
set to the programmable controller CPU on the QJ71MT91-mounted station.
The MODBUS extended file register size depends on the file register (ZR) size
set to the programmable controller CPU on the QJ71MT91-mounted station.
For details, refer to the QCPU user's manual (explanation, program
fundamentals).
POINT
Even if the slave (QJ71MT91) receives Write File Record (FC: 21) when the
programmable controller CPU's file register (ZR) is read-only (for example, when
stored on a Flash card), it will issue a normal response.
In this case, however, the action for Write File Record is not performed.
To write to the extended file register, check that the programmable controller CPU's
file register (ZR) is writable or not in advance.
MELSEC-Q
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