Mitsubishi QJ71MB91 - Page 186

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7.3 MODBUS(R) Device Assignment Parameter
7.3.3 QJ71MB91 buffer memory assignment
7
PARAMETER SETTING
1) The QJ71MB91 receives a "Read holding register 400500" request message
from the master.
2) The QJ71MB91 reads the data from its own buffer memory according to the
value set to the MODBUS device assignment parameter.
At this time, faster processing is executed since access is not affected by any
sequence scan.
3) The QJ71MB91 creates a response message and sends it to the master.
POINT
The programmable controller CPU device memory value can be stored in the
QJ71MB91 buffer memory, and the QJ71MB91 buffer memory value can be
stored in the programmable controller CPU device memory.
Data can be stored by either of the following:
• Automatic refresh setting on GX Configurator-MB ( Section 8.5)
• Transfer using intelligent function module devices (Un\G )
User's Manual (Function Explanation, Program Fundamentals) for
the CPU module used
Figure 7.10 MODBUS device and buffer memory
D300
400499
400500
400501
R
R
1)
2)
Programmable
controller CPU
No sequence
program required
Device memory
1234H
Auto refresh
QJ71MB91 (Slave function)
MODBUS device assignment parameter
Buffer memory
MODBUS device
User free area
3)
Create response
message to master
Request message (Read request for holding register 400500)
Response message (Holding register 400500 = 1234H)
R
MODBUS
Master device
RS-232, RS-422 or RS-485