How to work out what CRC calculation to use?

[craigcurtin]

Guys,

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 ?

regards

Craig

[craigcurtin]

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

How to calculate CRC-16 (Modbus)?

Hi everyone, I am trying to calculate CRC with a function I got from Node-RED forum, but when there is a 0 at the end or at the beginning of the CRC, it does not identify it, and I just get three bytes. The fact is that I do not want to download any node, only a function for the CRC-16 (Modbus) like a frame like this: 010600000001 + CRC Could anyone help me please? Thank you very much, Q.

Craig