Register Map Review Checklist for Manufacturers
A register map should be easy to read and hard to misunderstand. If the documentation is unclear, integrators will guess. That leads to support cases, failed projects, and unhappy customers.
Use this checklist before releasing a device.
Register map checklist
For every register or data point, check that the documentation clearly states:
- register address
- register type
- name of the value
- data type
- unit
- scaling
- signed or unsigned
- read or write access
- valid range
- default value if relevant
- byte order if multi-byte
- word order if multi-register
- any special states or fault values
Check the address format
Say clearly whether the addresses are raw offsets or numbers like 40001. Do not assume the user will know. This is one of the most common sources of mistakes.
Check the register type
Make it clear whether the value is in:
- coils
- discrete inputs
- input registers
- holding registers
Do not leave this for the reader to guess.
Check the data type
State whether the value is:
- 16-bit unsigned integer
- 16-bit signed integer
- 32-bit integer
- float
- bit field
This must be written clearly.
Check scaling and units
If the raw value needs scaling, say exactly how it works.
Example:
- raw value 253 = 25.3 °C
- divide by 10
Also state the unit for every measured value. For example temperature unit can be Fahrenheit, celsius or kelvin. That affects the outcome a lot.
Check multi-register values
If a value uses more than one register, explain how the registers are combined. State byte order and word order clearly.
Check write behavior
If a value can be written, document:
- allowed range
- allowed values
- what happens if the value is out of range
- whether changes apply immediately or after restart
Check exception behavior
If a request is not supported, say what happens. If the device returns Modbus exception codes, document them.
Check examples
Add at least one real example. A simple request and response example saves a lot of time for the user.
Final note
A good register map reduces support work. A bad one creates confusion even if the device itself works correctly.
Consulting
Manufacturers can hire me for help with Modbus device documentation, testing, and troubleshooting.