Meadow.Modbus

Meadow.Modbus is designed to be cross-platform, and does not require the use of Meadow.Core, meaning that it can be used in pretty much any modern .NET application.

It has been verified on hardware on the following platforms:

Feature	Platform	Notes
Modbus RTU Client	Meadow Feather F7	b6.2 or later
Modbus RTU Client	Windows 10	.NET 6
Modbus RTU Client	Raspberry Pi, Raspbian Buster	.NET 5, .NET 6 and Mono
Modbus TCP Client	Windows 10	.NET 6
Modbus TCP Client	Raspberry Pi, Raspbian Buster	.NET 5, .NET 6 and Mono
Modbus TCP Server	Windows 10	.NET 6

Usage Examples

Modbus RTU Client

This sample assumes you have a Thermostat connected over RS485 and configured to be at Modbus address 201.

Create a ModbusRtuClient instance, passing in the SerialPort for COM4 and DigitalOutputPort used for the enable.

var port = Device.CreateSerialPort(Device.SerialPortNames.Com4, 19200, 8, Meadow.Hardware.Parity.None, Meadow.Hardware.StopBits.One);
port.WriteTimeout = port.ReadTimeout = TimeSpan.FromSeconds(5);

var enable = Device.CreateDigitalOutputPort(Device.Pins.D02, false);
var client = new ModbusRtuClient(port, enable);

The Temco TSTAT8 uses holding registers for all of its interfacing. It has a lot of registers for reading or controlling just about every aspect of its operation. For our purposes we’ll only look at two of them: current temperature and current occupied setpoint. Since Modbus holding registers are ushort values, but the actual temperature and setpoint are in tenths of a degree, we have to do scaling in our application. For example a current temperature register reading of 721 equates to a temeprature of 72.1 degrees. Similarly if we want to set a setpoint of 69.5 degrees, we write 695.

To read the current temperature and output it to the console every 5 seconds, we can use a loop like this:

byte address = 201;

ushort tempRegister = 121; // current temp, in tenths of a degree

while (true)
{
    registers = await client.ReadHoldingRegisters(address, tempRegister, 1);

    Console.WriteLine($"Current temp: {registers[0] / 10f}");

    await Task.Delay(TimeSpan.FromSeconds(5));
}

Writing to a holding register is similar to the read shown above. Below is code that reads the setpoint, changes it with a write, then re-reads to verify the change:

byte address = 201;
ushort setPointRegister = 345; // occupied setpoint, in tenths of a degree

Console.WriteLine($"Reading setpoint holding register...");

var registers = await client.ReadHoldingRegisters(address, setPointRegister, 1);

Console.WriteLine($"Current set point: {registers[0] / 10f}");

var r = new Random();
var delta = r.Next(-20, 20);
var newSetpoint = (ushort)(registers[0] + delta);

Console.WriteLine($"Changing set point to: {newSetpoint / 10f}...");

await client.WriteHoldingRegister(address, setPointRegister, newSetpoint);

Console.WriteLine($"Re-reading thermostat holding registers...");

registers = await client.ReadHoldingRegisters(address, setPointRegister, 1);

Console.WriteLine($"Current set point: {registers[0] / 10f}");

Modbus TCP Client

Coming Soon!

Modbus TCP Server

Coming Soon!

License

Apache 2.0

See LICENSE File