Modbuzz - a Modbus slave emulator for testing purposes.

Modbuzz is a simple utility which emulates a Modbus slave. Currently only RTU is implemented.

Running the program

The pre-packaged versions of the program support Windows 10 x64 (or newer) and Debian 10 arm64 (or newer). Support is not guaranteed for other platforms. To run the program on other Linux distributions, consult the RCJP.SerialPortStream readme.

The program takes 5 arguments:

1. Serial port (e.g. COM3 on Windows or /dev/ttyUSB0 on Linux)
2. Baud rate (e.g. 9600)
3. Data bits (e.g. 8, but values 6-8 are allowed)
4. Parity (e.g. None, but None, Even, Odd, Mark, and Space are allowed, not case-sensitive)
5. Stop bits (e.g. One, but One, One5, and Two are allowed, not case-sensitive)

It then opens the serial port and starts responding to Modbus requests from a master. The emulated device parameters are as follows:

• Slave ID: 192 (0xC0)
• Registers:
  • Coil:
    • 10000 (0x2710, PLC: 10001): Enable random number generator
    • 10001 (0x2711, PLC: 10002): Enable logging (currently has no effect)
  • Discrete input:
    • 40000 (0x9C40, PLC: 40001): Current random number is greater than the last one
    • 40001 (0x9C41, PLC: 40002): Counter value overflowed on last tick
  • Holding register:
    • 20000 (0x4E20, PLC: 20001): Random lower bound
    • 20001 (0x4E21, PLC: 20002): Random upper bound
    • 20002 (0x4E22, PLC: 20003): Random range (if set to non-zero value, will cause the next random to be within this much of the last)
    • 20003-20004 (0x4E23-0x4E24, PLC: 20004-20005), size 2: 32-bit number register
    • 20005 (0x4E25, PLC: 20006): Writeable numeric value for float testing
  • Input:
    • 30000 (0x7530, PLC: 30001): Last random number generated
    • 30001 (0x7531, PLC: 30002): Request counter
    • 30002-30003 (0x7532-0x7533, PLC: 30003-30004): 32-bit random number

Registers 30000, 30001, 30002, and 30003 are updated on each read of 30000. If the value of 10000 is 0, value of 30000 will not change.

The program discards repeated consecutive reads to the same address. If you want to read a register twice, issue another read or write command to another register in-between.

Building the program

You can build the program in 2 flavours: self-contained single-file trimmed .NET application, or a .NET AOT binary. To deploy as the latter, pass -p:AOT_RELEASE=1 to dotnet publish.

For Linux, you must first compile native libraries for RJCP.SerialPortStream. Consult the project's readme for instructions.

To build a deployable executable, use dotnet publish. For example:

dotnet publish -c Release -r linux-arm64 -o publish-linux-arm64/ src/Emzi0767.Modbuzz.Feeder

The above command will create a Linux AArch64 (ARM64) binary for glibc-based systems. For Runtime IDs for other platforms, consult the .NET documentation.