Modbus can address register 0, but a successful read depends on the target device's register map. Do not assume that protocol support means the device maps data at that address.
Separate Protocol Addressing from the Device Map
The Modbus protocol supports address 0. The server device still determines whether that address contains a parameter. A request for an unmapped address cannot return valid process data.
| Target | Address 0 | Required decision |
|---|---|---|
| Third-party sensor or PLC | Unknown from the available evidence | Check its manufacturer register map. |
| Teltonika device running RutOS | No parameter mapped | Start with address 1 for the first documented parameter. |
Determine Whether Register 0 Is Readable
- Identify whether the request targets a Teltonika Networks device or a third-party sensor or PLC.
- Open the register map for that exact target device.
- Check whether the map explicitly assigns a parameter to address 0.
- If address 0 is unmapped, use the documented address for the required parameter and verify that the response contains valid data.
For a third-party device, the available evidence does not establish whether register 0 is mapped. Its own documentation controls the answer.
Apply the Teltonika RutOS Address Map
Teltonika RutOS does not define data at address 0. Its documented map begins at address 1, where the first real parameter is System Uptime. Configure the request with address 1 when reading that first available parameter.
This Teltonika-specific mapping must not be applied to unrelated sensors or PLCs. If a third-party map assigns data to address 0, a read may be valid because Modbus itself supports that address.
FAQ
Can Modbus read register 0?
Yes, the protocol supports address 0, but the target device must map a parameter there. Confirm the address in the device's register map.
Why does Teltonika register 0 return no valid data?
Teltonika RutOS maps no parameter at address 0. Its register map starts at address 1.
What is the first Teltonika RutOS Modbus register?
Address 1 is the first mapped address in the supplied evidence, and it contains System Uptime.