10 register map mistakes that break integrations

A device can have working Modbus communication and still be hard to integrate. The problem is often the register map.

Here are 10 common mistakes that cause trouble.

1. Address base is unclear

If the manual does not explain whether addresses are 0-based or 1-based, the user may read the wrong register.

2. Register type is unclear

The user must know whether the value is in holding registers, input registers, coils, or discrete inputs.

3. Data type is missing

Without the data type, the value cannot be interpreted correctly.

4. Scaling is missing

If the raw value needs scaling, state it clearly.

5. Signed or unsigned is not stated

This matters especially when values can go below zero.

6. Byte order is not stated

For values larger than one byte, this can change the result.

7. Word order is not stated

For 32-bit values stored in two registers, wrong word order leads to wrong readings.

8. Read or write access is unclear

The user must know what can be read and what can be written.

9. Units are missing

A number without a unit can be useless.

10. No examples are given

Examples help the user confirm that the data is read correctly.

Final note

A register map should remove doubt, not create it. If a user has to guess, the documentation is not complete enough.

Consulting

Manufacturers can hire me for help with Modbus device documentation, testing, and troubleshooting.