How to work out what CRC calculation to use?


I have an undocumented energy meter that i am reading from - i have snooped on the protocol and found information online about similar units so can make some assumptions about the data involved.

However i am wondering how - given the current data i work out what CRC algorithm they are using for me to inject my own data ?

For instance this is the request my Inverter makes to the energy meter every 200ms

03 03 00 61 00 17 55 F8

03 - ID of slave device
03 - Function code
00 61 - Start register
00 17 - number of registers (23)
55 F8 - CRC

How do i work out what Algo it is using to calculate the CRC ?



I found this forum thread and it appears to work with each of my requests so i assume now this is using standard Modbus CRC16


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