0121-11 Monarco HAT Modbus RTU Loopback USB

Example Projects > 0121 Monarco HAT > 0121-11 Monarco HAT Modbus RTU Loopback USB

Modbus RTU data loopback, Monarco HAT and USB RS-485 adapter

This folder contains the source files for the loopback test of RS-485 communication on Raspberry Pi with Monarco HAT and a USB RS-485 dongle. Data is exchanged over the Modbus RTU protocol.

Both the master and slave stations are implemented on the Raspberry Pi itself, the project is meant only for testing and debugging purposes.


  • REXYGEN Runtime Core, MonarcoDrv and MbDrv modules must be installed and running on the Raspberry Pi to run the example.

Running the examples

  • The *exec.mdl file is the project main file.
  • Open it with REXYGEN Studio, compile and download it to the target device.
  • Switch to Watch mode and observe the algorithm.

Modbus registers##

Data out (from the master's point of view)

Register No. Meaning Data range
2048 Unsigned integer 0 .. 65535
2049 Signed integer -32768 .. 32767
2050 Unsigned integer 0 .. 65535
2051 Signed integer -32768 .. 32767
2052-2053 Floating-point number -3.4E+38 .. 3.4E+38
2054-2057 Double precision floating-point number -1.7E+308 .. 1.7E+308

Adding signals and changing Modbus register mapping

Go to Modbus driver configuration (MBM block for the master, MBS block for the slave) and press "Configure" for Modbus registers configuration. Make sure to read the Modbus driver documentation (see below).


Additional information

  • Visit the REXYGEN webpage for more information about the example projects and developing advanced automation and control solutions using REXYGEN.