max485-raspberry-nodejs

Node.js library for Modbus RTU communication over RS485 using MAX485 transceivers on Raspberry Pi.

Installation

npm install max485-raspberry-nodejs

Requirements

• Node.js >= 14.0.0
• Linux (tested on Raspberry Pi)
• RS-485 Serial Port

Usage Example

const ModbusRTU = require('max485-raspberry-nodejs');

// Create Modbus device instance
// Parameters:
// - port: serial port path (e.g., '/dev/serial0' or '/dev/ttyUSB0')
// - baudRate: communication speed (e.g., 9600)
// - dePin: GPIO pin number for DE (Driver Enable)
// - rePin: GPIO pin number for RE (Receiver Enable)
const device = new ModbusRTU('/dev/serial0', 9600, 17, 27);

async function example() {
    try {
        // Read coils (function 0x01)
        const coils = await device.readCoils(1, 0, 4);
        console.log('Coils state:', coils);

        // Write single coil (function 0x05)
        await device.writeCoil(1, 0, true);

        // Write multiple coils (function 0x0F)
        await device.writeMultipleCoils(1, 0, [true, false, true, false]);

        // Read holding registers (function 0x03)
        const registers = await device.readHoldingRegisters(1, 0, 4);
        console.log('Registers state:', registers);

        // Write single register (function 0x06)
        await device.writeRegister(1, 0, 123);

        // Write multiple registers (function 0x10)
        await device.writeMultipleRegisters(1, 0, [50, 100, 150, 200]);

    } catch (error) {
        console.error('Error:', error.message);
    } finally {
        // Close connection
        device.close();
    }
}

example();

API

Constructor

new ModbusRTU(port, baudRate, dePin, rePin)

• port (string): Serial port path
• baudRate (number): Communication speed
• dePin (number): GPIO pin number for DE signal
• rePin (number): GPIO pin number for RE signal

Methods

Reading Data

• readCoils(slaveId, startAddr, count): Read coils (function 0x01)
• readDiscreteInputs(slaveId, startAddr, count): Read discrete inputs (function 0x02)
• readHoldingRegisters(slaveId, startAddr, count): Read holding registers (function 0x03)
• readInputRegisters(slaveId, startAddr, count): Read input registers (function 0x04)

Parameters:

• slaveId (number): Modbus device address (1-247)
• startAddr (number): Starting address
• count (number): Number of elements to read

Returns: Promise with array of values (boolean for coils/inputs, number for registers)

Writing Data

• writeCoil(slaveId, addr, value): Write single coil (function 0x05)
• writeRegister(slaveId, addr, value): Write single register (function 0x06)
• writeMultipleCoils(slaveId, startAddr, values): Write multiple coils (function 0x0F)
• writeMultipleRegisters(slaveId, startAddr, values): Write multiple registers (function 0x10)

Parameters:

• slaveId (number): Modbus device address (1-247)
• addr/startAddr (number): Address to write to
• value (boolean/number): Value to write
• values (Array): Array of values to write

Returns: Promise

Connection Management

• close(): Closes the connection to the device

Error Handling

All methods (except close()) return a Promise. In case of an error, the Promise is rejected with an appropriate error message.

License

MIT