Modbus student needing help with Modbus question

Hello to all Modbus experts from a very much novice.
I am a student and am hoping to get some guidance on a question in which I am unsure of.
Any help would be greatly appreciated.
Thanks Cosmo


You can find request and response examples right in the Modbus spec here:

Take a look at section 6.3 for the 03 (0x03) Read Holding Registers example.

Of course, with Modbus ASCII, all packets will start with the colon ':' character and end with the carriage return 'CR' and line feed 'LF' characters.

The only hard part is calculating the LRC (note that you are incorrectly calling the LRC a CRC - Modbus RTU uses a CRC, Modbus ASCII uses a LRC). Details on this can be found in Appendix B of the Modbus Serial Line Protocol and Implementation Guide here: