Technical Guide P92x/EN CT/E11
Modbus Protocol
MiCOM P921-P922-P923 Page 9/118
Error code :
Among the 8 exception codes of the MODBUS protocol, the MiCOM relay manages
two of them :
· code 01 : Function code unauthorised or unknown.
· code 03 : A value of the data field is unauthorised (incorrect code).
- Control of pages being read.
- Control of pages being written.
- Control of address in pages.
- Length of request messages.
CRC16:
The CRC16 value is calculated by the slave.
1.4 Modbus request definition used to retrieve the disturbance records
To retrieve a disturbance record, the following requests must be done in the exact
given order :
1. (optional) : Send a request to know the number of disturbance records
available in the saved RAM.
2. To retrieve the data of one channel:
2a – (compulsory) : Send a service request specifying the record number
and the channel number which have to be retrieved.
2b – (compulsory) : Send requests to retrieve the data of a disturbance
record channel as many time as needed.
2c – (compulsory) : send a request to retrieve the index frame.
3. Process the same operation (as described in the item 2) for each channel.
1.4.1 Request to know the number of available disturbance records in the Saved RAM.
Slave number Function code Word address Word number CRC
xx 03h 3Dh 00 00 24h xx.........xx
This request may be answered an error message with the error code :
EVT_NOK (0F) : No record available.
NOTA : If there is less than 5 records available, the answer will contain
zero value in the non-used words.
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