Mitsubishi QJ71MB91, User Manual

Page: 19 / 372

1
OVERVIEW
1.1 Features
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CIFICA
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MODB
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FUNC
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PER
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UTIL
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(G
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B)
(b) Communication using dedicated instruction
Dedicated instructions can be used to make communication from sequence
programs at any timing.
The following dedicated instructions are available for the QJ71MB91. (
CHAPTER 10)
1) MBRW instruction
Reads or writes MODBUS device data from or to a slave.
This enables reading slave data to the programmable controller CPU device
memory or writing programmable controller CPU data to slaves.
2) MBREQ instruction
The user-determined request message format (function code + data unit) can
be issued to the slaves.
Figure 1.2 Communication using dedicated instruction
[Z.MBRW ]
Command
QJ71MB91
(Master
function)
400500
Response Message ( Holding register 400500= 1234H)
Programmable
controller CPU
Device memory
1234
H
Request message
(Read request for holding register 400500)
Response message
(Holding register 400500 = 1234
H
)
1234
H
Holding register
R
MODBUS Slave device
RS-232, RS-422 or RS-485