Protocol Data Unit Formats By Functions - Mitsubishi QJ71MB91 User Manual

4
MODBUS(R) STANDARD FUNCTIONS

4.3 Protocol Data Unit Formats by Functions

This section describes MODBUS
(1) Precautions
4
- 15 4.3 Protocol Data Unit Formats by Functions
(a) Device number specified in messages
When specifying a device number in a message, specify it as "(Device number) -
1".
However, this does not apply to the file and device numbers specified for reading/
writing the extended file register.
(Example) When reading input 32 (100032) with Read Discrete Inputs (FC: 02)
Function code
Function code
Head input number
02
H
(H)
Specify 31 (001F ) for the head input number
H
to read the input 32 (100032) status.
Figure 4.6 Specifying the MODBUS
The device number to be stored in the response message is "(Device number of
actually read/written device) - 1".
(b) When the QJ71MB91 receives a broadcast request message
Although the processing (read/write, diagnostics, etc.) requested by the request
message is performed, no response message is sent to the master.
(c) When the QJ71MB91 receives a request message in the listen only mode
The request message is discarded except for a particular case.
To receive the request message, change it to the online mode.
( Section 4.11.5)
protocol data unit formats used in the QJ71MB91.
Data
Read points
001F
H
(L)
(H)
device number
0001
H
(L)