Frame Specifications - Mitsubishi FX3U Series User Manual

FX Series Programmable Controllers
3U
User's Manual - MODBUS Serial Communication Edition
7.2

Frame Specifications

The following shows the frame specifications for the MODBUS protocol.
Address field
The following table details the frame specification for the MODBUS Protocol.
Area name
Address field
Function code
Data
Error check *1
*1. The error check method differs depending on the frame mode. See Subsection 7.2.1.
Note
Refer to the Subsection 7.2.1 for the data size of each area.
Function code
MODBUS Protocol Data Section
Section 7.3 to section 7.18
[When the master sends a request message to a slave]
0: Sends a request message to all the slaves. (Broadcast)
1 to 247: Sends a request to a specific Slave number.
[When the slave sends a response message to the master]
The host station number is stored when sending a response message.
Note: 247 is the MODBUS maximum address number. The FX
address from 1 to16 stations within this range.
[When the master sends a request message to a slave]
The master specifies the number of the action to be taken by the slave.
[When the slave sends a response message to the master]
A requested function code is stored in the case of normal completion. The most
significant bit turns ON in the case of error completion.
[When the master sends a request message to a slave]
The information needed to execute the action specified by a function code is stored.
[When the slave sends a response message to the master]
The execution result of the action specified by a function code is stored. An exception
code is stored when failed.
The node adds the check code automatically to all transmitted messages and
recalculates the check code for any received message. The received message is
discarded if it has an error.
7 MODBUS Standard Commands
7.2 Frame Specifications
Data Error check
Description
3U
MODBUS Master can
10
43
1
2
3
4
5
6
7
8
9