Force Listen Only Mode (Sub-Function Code: 04H) - Mitsubishi Electric MELSEC iQ-R Series Reference Manual

Force listen only mode (sub-function code: 04H)

Operation description
Places a slave into the offline mode.
Used when disconnecting a slave from the network.
When C24 is set in the listen only mode, the status is as follows:
• Ignores all request messages except for those of restart communications option. (Page 23 Restart communications
option (sub-function code: 01H))
• Stops counting of the diagnostic counter. (Page 21 Checking communication conditions using a diagnostic counter)
• Continues recording with the communications event log. (Page 39 Get Communications Event Log (FC: 0CH))
Request message format (from master to slave)
Function code Sub-function code
08H
(H)
Response message format (from slave to master)
■ When completed successfully
No response message is returned because the listen only mode (offline status) is active.
■ When completed with an error
Function code Data
Exception code
88H
Whether the C24 has been switched to listen only mode or not can be checked in the 'Communications mode'
of the buffer memory (Un\G32525/32589).
• 0000H: Online mode
• 0001H: Listen only mode
The listen only mode can be changed to online mode by either of the following:
• Restart communications option (Page 23 Restart communications option (sub-function code: 01H))
• Turn the power OFF and ON, or reset the programmable controller CPU.
3 MODBUS STANDARD FUNCTION DETAILS
26
3.8 Diagnostics (FC: 08H)
(0004H)
(L) (H)
Data
(0000H)
(L)