Mitsubishi Electric QJ71MB91 User Manual page 20

1
OVERVIEW
Programmable
controller CPU
Command
[Z.MBRW
Device memory
1234H
1
- 2 1.1 Features
(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.
QJ71MB91
(Master
function)
]
Figure 1.2 Communication using dedicated instruction
Request message
(Read request for holding register 400500)
Response message
(Holding register 400500 = 1234H)
RS-232, RS-422 or RS-485
MODBUS Slave device
Holding register
400500 1234H