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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 packets is changed by the command
(function) contents.
The space between messages must support the following:
DDC to Drive
Command message
Slave Address
Set the Drive address from 0 to 32. If 0 is selected, commands from the master will be broadcast (i.e., the Drive will not return
responses).
Function Code
The function code specifies commands. There are four function codes, as shown below.
Function Code
(Hexadecimal)
03H
Reading/Holding Register Contents
06H
Write In Single Holding Register
08H
Loopback Test
10H
Write In Several Holding Registers
* Minimum bytes for a normal Response Message (error response message is always 5 bytes).
Data
Configure consecutive data by combining the storage register address (test code for a loopback address) and the data the
register contains. The data length changes depending on the command details.
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Slave address
Function code
Error check
Fig D.4 Message Format
Drive to DDC
Response message
H5-06
24 bits long
24 bits long
setting
Fig D.5 Message Spacing
Table D.3 Modbus Function Codes
Function
Communications D - 5
Data
DDC to Drive
Command message
5 ms min.
Command Message
Min.
Max.
(Bytes)
(Bytes)
8
8
8
8
8
8
11
41
Time (Seconds)
Response Message
Min.*
Max.
(Bytes)
(Bytes)
7
37
8
8
8
8
8
8
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