Function Code 08 - Loopback Message - Honeywell HC900 User Manual
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Modbus/TCP & Modbus RTU Function Codes
Function Code 08 - Loopback Message
4.9 Function Code 08 - Loopback Message
Description
Echoes received query message.
Query
Message can be any length up to half the length of the data buffer minus 8 bytes.
Example: 00 08 01 02 03 04
TCP Example
RTU Example
Response
Example: 00 08 01 02 03 04
TCP Example
RTU Example
36
Query message format for function code 08
Slave
Function
Any data, length limited to approximately half
Address
Code
(00 for TCP)
00
08
01
08
Response message format for function code 08
Slave
Function
Address
Code
(00 for TCP)
00
08
01
08
HC900 Process Controller Communications User Guide
the length of the data buffer
01 02 03 04
01 02 03 04
Data bytes received
01 02 03 04
01 02 03 04
CRC
CRC
(RTU)
(RTU)
CRC
CRC
CRC
CRC
(RTU)
(RTU)
CRC
CRC
Revision 13
April 2017
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