(0X08) Diagnostics - Hitachi HX-RIO3 Series User Manual

47
A.3.7. 8 (0x08) Diagnostics
MODBUS function code 08 provides a series of tests for checking the communication system between a
client (Master) device and a server (Slave), or for checking various internal error conditions within a server.
The function uses a two–byte sub-function code field in the query to define the type of test to be performed.
The server echoes both the function code and sub-function code in a normal response. Some of the
diagnostics cause data to be returned from the remote device in the data field of a normal response.
•
Request
Field name
Start of Frame
Slave Address
Function Code
Sub-Function Hi
Sub-Function Lo
Data Hi
Data Lo
Error Check (CRC/LRC)
End of Frame
•
Response
Field name
Start of Frame
Slave Address
Function Code
Sub-Function Hi
Sub-Function Lo
Data Hi
Data Lo
Error Check (CRC/LRC)
End of Frame
✓ Sub-function 0x0000(0) Return Query Data
The data passed in the request data field is to be returned (looped back) in the response.
The entire response message should be identical to the request.
Sub-function
0x0000(0)
Example RTU
- t1-t2-t3
0x07 0x07
0x08 0x08
0x00 0x00
0x00 0x00
0x11 0x11
0x22 0x22
- 0x6C, 0x24
- t1-t2-t3
Example RTU
- t1-t2-t3
0x07 0x07
0x08 0x08
0x00 0x00
0x00 0x00
0x11 0x11
0x22 0x22
- 0x6C, 0x24
- t1-t2-t3
Data Field (Request)
Any
Data Field (Response)
Echo Request Data
HX-RIO3 Series
Description