Message Format; Slave Address; Function Code; Modbus Function Code - YASKAWA F7 User Manual

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Message Format

In Modbus communication, the master sends commands to the slave, and the slave responds. The message format is
configured for both sending and receiving as shown below. The length of the data packet is controlled by the command
(function) contents.
The space between messages must support the following:

Slave Address

Set the Drive address from 0 to 20 Hex. If 0 is selected, commands from the master will be broadcast (i.e., the Drive will not
return a response message).

Function Code

The function code specifies command type. There are four function codes, as shown below.
Function Code
(Hexadecimal)
03H
06H
08H
10H
* Minimum bytes for a normal Response Message (error response message is always 5 bytes).
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PLC to Drive
Command message
24 bits long
Table D.3 Modbus Function Codes
Function
Reading/Holding Register Contents
Write In Single Holding Register
Loopback Test
Write In Several Holding Registers
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Slave address
Function code
Data
Error check
Fig D.4 Message Format
Drive to PLC
Response message
H5-06
24 bits long
setting
Fig D.5 Message Spacing
Command Message
Min.
(Bytes)
8
8
8
11
Communications D - 5
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PLC to Drive
Command message
Time (Seconds)
5ms min.
Response Message
Max. Min.*
(Bytes) (Bytes)
8 7
8 8
8 8
41 8
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Max.
(Bytes)
21
8
8
8