Appendix 4 MODBUS Communication
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Instructions example
Read Holding Registers
[03H]
The contents of the specified number are read out in MODBUS address. The holding
register contents are divided into the high 8-bit and low-order 8-bit, and become the data
in the response message in that order.
Example: Read out the slave 1 running status
Command Message
Normal Response Message AbnomalResponse Message
Slave Address
01
Function Code
03
Starting
No.
Upper
00
Lower
20
Quantity
Upper
00
Lower
01
CRC
Upper
85
Lower
C0
Slave Address
01
Function Code
03
No. of Data
02
Data
Upper
00
Lower
C1
CRC
Upper
79
Lower
D4
Slave Address
01
Function Code
83
Error Code
03
CRC
Upper
01
Lower
31
Note：
No. of Data is double
Command Message
Quantity
Write-in to single register [
06H]
Single specified data item is written in the specified register, specified data is stored in
the specified register. It is necessary to arrange the written data items in the MODBUS
register address table in the order of the upper 1 byte and the lower 1 byte.
Example: Start slave 1.
Command Message
Normal Response Message AbnomalResponse Message
Slave Address
01
Function Code
06
Starting
No.
Upper
00
Lower
01
Quantity
Upper
00
Lower
01
CRC
Upper
19
Lower
CA
Slave Address
01
Function Code
86
Error Code
02
CRC
Upper
C3
Lower
A1
Slave Address
01
Function Code
06
Starting
No.
Upper
00
Lower
01
Quantity
Upper
00
Lower
01
CRC
Upper
19
Lower
CA
Feedback loop Test
[08H]
The transmitted message is returned unchanged as a response message. This test is used
for checking the signal communication between master and slave. Test data can use any
value.
