Setting Modbus IDs

Like all Modbus devices, Bus Probes connected to the same RS485 bus must be assigned unique Modbus IDs.

The Modbus ID of each probe is stored in its register 200. IDs must be in the range between 1 and 247. Attempts to set a value outside of this range will be ignored.

Perhaps the most convenient way of setting the IDs of Bus Probes is the Bus Probe Test App, which requires Tibbo's Web485 board(1) and a Chromium-based web browser (Chrome, Chromium, Edge, Opera). Alternatively, you can use a TPS2(G2) system running one of the two Bus Probe testing apps provided by Tibbo.

You can also use any suitable Modbus software to write a new value into the ID register. Since PCs do not come equipped with RS485 ports, you will need to procure a USB-to-RS485 cable. You will also need a DC power source to power the Probes (5~12V voltage range recommended).

For example, if you want to change the ID of a Bus Probe from 1 to 9, the Modbus request would look like this:

01 06 00 C8 00 09 C8 32

It is only possible to alter the ID register when the MD button(2) is pressed. Therefore, you must press and hold the MD button when sending the command to write register 200.

 

  1. The Web485 board works not only with PCs and Macs, but also Android smartphones.
  2. Each Bus Probe comes with a metal pin that makes pushing and holding down the MD button easier.

Default Modbus IDs

The default Modbus ID of a Bus Probe depends on its type:

  • 0x40 for BP#01 (ambient temperature sensor)
  • 0x41 for BP#02 (relative humidity and temperature sensor)
  • 0x42 for BP#03 (ambient light sensor)
  • 0x43 for BP#04 (3-axis accelerometer)
  • 0x44 for BP#05 (flood/leak sensor)