X02 return diagnostic register, X04 force listen only mode, X0a clear counters – Watlow CLS200, MLS300 and CAS200 User Manual
Page 34: X0b return bus message count, X0c return bus communication error count
28 Communications Specification
Chapter 2: Modbus-RTU Protocol
response is returned. This function is the only one that
brings the port out of Listen Only Mode. If the port is not
currently in Listen Only Mode, a normal response is
returned. This occurs before the restart is executed.
Subfunction
Data Field (Query)
Data Field (Response)
x00 01
x00 00
Echo Query Data
x00 01
xFF 00
Echo Query Data
x02
Return Diagnostic Register
•
The contents of the slave’s 16-bit diagnostic register are
returned in the response.
Subfunction
Data Field (Query)
Data Field (Response)
x00 02
x00 00
Diagnostic Register
Contents
x04
Force Listen Only Mode
•
Forces the addressed slave to its Listen Only Mode for
Modbus-RTU communications. This isolates it from the
other devices on the network, allowing them to continue
communicating without interruption from the addressed
slave. No response is returned.
•
When the slave enters its Listen Only Mode, all active com-
munication controls are turned off. The ready watchdog
timer is allowed to expire, locking the controls off. While in
this mode, any Modbus-RTU messages addressed to the
salve or broadcast are monitored, but no actions will be
taken and no responses will be sent.
•
The only function that will be processed after the mode is
entered will be the Restart Communications Option func-
tion (function code 8, subfunction 1).
Subfunction
Data Field (Query)
Data Field (Response)
x00 04
x00 00
No Response
Returned
x0A
Clear Counters
•
Clears all Communication Event counters. Counters are
also cleared upon power-up.
Subfunction
Data Field (Query)
Data Field (Response)
x00 0A
x00 00
Echo Query Data
x0B
Return Bus Message Count
•
The response data field returns the quantity of messages that
the slave has detected on the communications system since
its last restart, clear counters operations, or power-up.
Subfunction
Data Field (Query)
Data Field (Response)
x00 0B
x00 00
Total Message Count
x0C
Return Bus Communication Error Count
•
The response data field returns the quantity of CRC errors
encountered by the slave since its last restart, clear counters