Modbus Commissioning & Handover Documentation
A Modbus installation isn't finished when it answers a poll — it's finished when the next technician can service it without rediscovering the bus from scratch. That takes an address list, a register map and a settings sheet, not memory.
The handover package, step by step
Build the address list
Map every RTU slave address (1-247) to a physical device and location, so nobody has to poll blind during a fault call to work out what answers where.
Attach the register map per device
Record which holding and input registers, function codes and addressing convention each device uses, referencing the manufacturer's documentation directly.
Document baud, parity and stop bits
Write the shared serial settings for the segment on one sheet, since every device on an RS-485 line must match exactly or communication fails outright.
Run and log poll tests
Poll the registers that matter — read and write — and log what came back before sign-off, so commissioning is evidenced rather than assumed.
What a documented Modbus handover protects
core deliverables
Address list, register map, settings sheet, poll-test log and bus labelling — the five pieces that stop a fault call turning into bus archaeology.
Address list mapped to physical devices
Every slave address from 1 to 247 tied to a device name and location, so nobody polls blind to find out what's on the bus.
Register map per device
Which holding and input registers, which function codes (FC03/04 read, FC06/16 write) and which addressing convention — 0-based or 40001-style — each device expects.
Serial settings sheet
Baud rate, parity, data bits and stop bits recorded once for the segment, because every device on the RS-485 bus has to share the same values.
Poll-test log
A record of which registers were read and written during commissioning and what came back, so correct behaviour is proven rather than assumed.
Bus labelling matching the documentation
Physical labels at each device and at both termination points use the same names and addresses as the paperwork, not a separate private scheme.
Handover package contents
What we recommend every Modbus commissioning finishes with.
- Address list — slave ID 1-247 mapped to device and physical location
- Register map per device — function codes, register types, addressing convention
- Serial settings sheet — baud rate, parity, data/stop bits (or TCP port and IP for Modbus TCP)
- Poll-test log confirming each register reads and writes as expected
- Bus and cable labelling matching the documentation set
Frequently asked questions
What should a Modbus handover package include?
At minimum: an address list mapping each slave ID to a physical device, a register map per device, a settings sheet with baud rate, parity and stop bits (or port and IP for Modbus TCP), a poll-test log, and bus labelling that matches the paperwork.
Why does the address list matter more for Modbus than for other buses?
A Modbus RTU address is just a number from 1 to 247 with no built-in device identity attached. Without a documented list, a technician has to poll addresses blind to work out which physical device answers to which ID.
What's the difference between holding registers and input registers, and why note it?
Holding registers (function code 03) are read and write; input registers (function code 04) are read-only. Both are 16-bit numeric values, so it's easy to mix them up — documenting the type and function code per point avoids write attempts that fail silently.
Why record baud rate, parity and stop bits on a separate sheet?
Every device on an RS-485 segment must use identical serial settings or the bus won't communicate at all. A dedicated settings sheet lets a technician configure a replacement device or a new master correctly without trial and error.
What does a poll-test log prove that a working system on handover day doesn't?
A bus that 'seems fine' at handover may only have been exercised on the points used that day. A poll-test log records exactly which registers were read and written and confirms the result, giving a paper trail for any later dispute about what was actually commissioned.
Need a second pair of eyes on your Modbus documentation?
Our engineers work with integrators and panel builders across the EU — talk to us about commissioning documentation, register maps or your next panel build.