ModBus Mode Communications
Append
ix
B
B–28
When the Write Holding Register command cannot be executed normally, refer to the
exception response.
Loopback Test [08h]:
This function checks a master-slave transmission using any test data. An example follows:
• Send test data to an inverter having slave address “1” and receiving the test data from the
inverter (as a loopback test).
The test subcode is for echo (00h,00h) only and not available to the other commands.
Query:
Note 1:
Broadcasting is disabled.
Note 2:
The starting coil number is one
less than the number of the coil to
be read first.
Response:
No.
Field Name
Example
(hex)
1
Slave address *1
05
2
Function code
06
3
Register start number
(high order) *2
12
4
Register start number
(low order) *2
02
5
Change data (high
order)
00
6
Change data (low order)
32
7
CRC-16 (high order)
AD
8
CRC-16 (low order)
23
No.
Field Name
Example
(hex)
1
Slave address
05
2
Function code
06
3
Register start number
(high order)
12
4
Register start number
(low order)
02
5
Change data (high
order)
00
6
Change data (low order)
32
7
CRC-16 (high order)
AD
8
CRC-16 (low order)
23
Query:
Note 1:
Broadcasting is disabled.
Response:
No.
Field Name
Example
(hex)
1
Slave address *1
01
2
Function code
08
3
Test subcode (high
order)
00
4
Test subcode (low
order)
00
5
Data (high order)
Any
6
Data (low order)
Any
7
CRC-16 (high order)
CRC
8
CRC-16 (low order)
CRC
No.
Field Name
Example
(hex)
1
Slave address
01
2
Function code
08
3
Test subcode (high
order)
00
4
Test subcode (low
order)
00
5
Data (high order)
Any
6
Data (low order)
Any
7
CRC-16 (high order)
AD
8
CRC-16 (low order)
23
