A device on the bus and no documentation, or documentation that doesn't match? ModbusManager finds it. Scan slave IDs, sweep address ranges, and auto-detect baud rate and parity when the settings are unknown — for RTU and TCP. Then read the registers in the same tool, decoded in every word order at once.
Windows 10/11 · RTU, ASCII & TCP · one-time license · 14-day trial
Unlike BACnet, Modbus has no built-in discovery. The master is supposed to already know every device, its address, and its serial settings. When it doesn't — a spare panel, an undocumented meter, a drive with the wrong DIP switches — the only way forward is methodical scanning: try the addresses, try the settings, see what answers. ModbusManager does all three, in one place.
You know the serial settings but not which slave IDs are live. Slave Scan walks the ID range (1–247) and reports every device that responds — even ones that only return an exception, which still proves they're there.
The device answers, but you don't have its register map. Address Scan sweeps a range of registers and shows which hold data, so you can rebuild the map from the device itself when the manufacturer's PDF is lost or wrong.
The hardest case: you don't know the baud rate, parity or slave ID. Auto-detect tries the combinations (9600/19200/38400…, none/even/odd, 1/2 stop) and reports what the device replies on — in standard 9600 8N1 form. It even guesses the word order from the first register pair. On TCP it scans Unit IDs behind a gateway.
CAS Modbus Scanner is a good, genuinely free discovery tool — if all you need is to find devices and read registers for a few minutes, it does that well. The difference shows up once discovery is done and you need to keep working with what you found.
| ModbusManager | CAS Scanner | |
|---|---|---|
| Scan slave IDs / address ranges | ✓ | ✓ |
| Auto-detect baud & parity | ✓ | ✓ |
| RTU, ASCII & TCP | ✓ | ✓ |
| Word order both ways (ABCD & CDAB, big & little endian) | ✓ | little-endian only |
| Save / export the register map you found | ✓ CSV, XLSX, PDF | — debug only |
| Snapshot & diff (what changed) | ✓ | — |
| Slave simulation (act as a device) | ✓ | — |
| Dashboard HMI, trends, alarms | ✓ | — |
| Combine several devices into one map (gateway) | ✓ | — |
| Price | from $49 one-time | free |
The comparison points about CAS (debug-only, little-endian word order) come from its own users and documentation. It's a fine tool for a quick look; ModbusManager is built for the work that comes after.
A 32-bit float spans two registers, and manufacturers don't agree on the order — ABCD, CDAB, BADC, DCBA. Guess wrong and the number is nonsense. In ModbusManager you right-click any 32-bit value and see all four interpretations at once, as both float and integer. The one that looks like a real reading tells you the order. CAS Scanner shows little-endian only, so a big-endian device reads wrong with no obvious fix.
If you just need to confirm a device is alive, read a handful of registers once, and move on — CAS Scanner is free, needs no license, and does exactly that. If your devices are all little-endian and you never need to save the map, it may be all you want. ModbusManager earns its price when discovery is the start of the job: documenting the register map, monitoring live values, simulating a device, or building an HMI on top.
Once you've found a device, these walk through the register maps and gotchas for common hardware:
Download the trial, plug in your USB-RS485 adapter, and hit Auto-detect. If it answers on the bus, ModbusManager will find it.
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