CRC and Modbus checks

CRC and Modbus checks

CRC failures are usually caused by one of four things: wrong payload bytes, wrong byte order, wrong CRC algorithm parameters, or missing line/frame boundaries.

Recommended workflow:

1. Copy the exact Hex payload without the CRC bytes.
2. Select the expected CRC algorithm, such as CRC-16/MODBUS when the device uses Modbus RTU.
3. Compare width, polynomial, initial value, xorout and reflection settings if the supplier document lists them.
4. Append the calculated CRC in the byte order required by the protocol.
5. Send the frame and compare the raw response bytes.

If a device returns nothing, first confirm the physical link and serial parameters. CRC debugging only helps after the device can actually receive the frame.