Hey Kalquape,

thnx for going inside to this problem. If I can only say my opinion, I think that he is afraid if his Slave need 16 bit CRC, if MB_Master can implement this 16 bit CRC. I must say, I don't know, maybe if I'll have my CM RS-232 in few days, I'll make some tests.

Update: but probably as you said heh, there is simply standard CRC implemented, but really I don't know if his 16-bit CRC isn't another format, but if yes this I can't believe  I think that this will be ok.

Thank you for Your support Kaulquappe and Duris.

Yes, I am going to implement Modbus RTU. Previously I had just really little experience with Modbus RTU and CRC checking is a new to me (I have't heard about CRC before).
Due to this reason I'm afraid if the PLC takes care of CRC check and if it uses the same CRC calculation system as the slave drive (just as Duris_I said).

On the forum I found that pressure transmitters from KELLER are using Modbus RTU via RS485. One user (Radastan) claims that KELLER device communicates with S7-1200 without problems (his problems were solved). I compared CRC calculations of KELLER device with calculations on the drive that I'm about to order. Both calculation methods give the same result thus I guess my PLC --> drive communication will be OK.

I am glad that Siemens takes care about the CRC check.
Thank You for support .

New question published by Sick097 is split to a separate thread with the subject Writing program to calculate CRC - what is wrong?.

Best regards
Jen_Moderator