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3 MODBUS STANDARD FUNCTION DETAILS
3.10 Get Communications Event Log (FC: 0CH)
Communications event log
When the get communications event log (FC: 0CH) is received from the master, C24 returns the following data of the buffer
memory.
• 'Communications event log 1 to 64' (Un\G32544 to Un\G32575/Un\G32608 to Un\G32639)
The number of communications event logs can be checked in the buffer memory 'Communications event log count'
(Un\G32543/Un\G32607).
If the number of communications event logs exceeds 64, the oldest log is deleted and the latest log is stored to
Communications event log 0.
Communications event logs are stored in the buffer memory at the following timing.
The communications event can be cleared by either of the following:
• Clear setting of the communications event log with the restart communications option. (Page 23 Restart
communications option (sub-function code: 01H))
• Turn the power OFF and ON, or reset the programmable controller CPU.
Timing to be stored in the buffer
memory
Description
When receiving a request message C24 stores the communications event log before executing the processing of the request message.
For the relevant communications event, '1' is stored.
• b0: Unused (Fixed to 0)
• b1: Communication error
• b2, b3: Unused (Fixed to 0)
• b4: Bus character overrun error
• b5: In listen only mode
• b6: Broadcast message reception
• b7: Fixed to 1
When sending a response message C24 stores the communications event log after sending the response message.
For the relevant communications event, '1' is stored.
• b0: Message error (exception code 01H to 03H)
• b1: Processing interruption (exception code 04H)
• b2 to b5: Unused (Fixed to 0)
While the occurrence of busy status (exception code 05H to 07H) is stored for the MODBUS protocol, '0' is
stored for C24 because this kind of events does not occur in it.
• b6: Fixed to 1
• b7: Unused (Fixed to '0')
When switching to the listen only mode C24 stores the communications event log when switching to the listen only mode.
04H is stored to the communications event log.
When processing restart communications option C24 stores the communications event log when processing the restart communications option.
00H is stored to the communications event log.
10001/0 1/0 1/0 1/0
b0b1b2b3b4b5b6b7
b0b1b2b3b4b5b6b7
0001001/01/0
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