Détail du package

modbus-webserial

anttikotajarvi903MIT0.10.1

Tiny TypeScript library for speaking Modbus-RTU from the browser via Web Serial

modbus, rtu, webserial, browser

readme

modbus-webserial

Tiny zero-dependency library for communicating with a Modbus-RTU serial device from the browser via WebSerial.

npm size dependencies CI License types esm

Install

npm install modbus-webserial

Usage

Connect → read/write in browser

import { ModbusRTU } from 'modbus-webserial';

// Prompt the WebSerial dialog and open port
const client = await ModbusRTU.openWebSerial({ baudRate: 9600 });
client.setID(1);

// Read holding registers 0x00 and 0x01
const { data } = await client.readHoldingRegisters(0, 2);
console.log('HR0=', data[0], 'HR1=', data[1]);

// Write values to holding registers 0x00 and 0x01
await client.writeRegisters(0, [0x0A, 0x0B]);

Can also be used without WebSerial for building modbus frames in any environment

import {
  buildReadHoldingRegisters,
  buildWriteRegisters
} from 'modbus-webserial';

// Build a “Read Holding Registers” frame (ID=1, addr=0, qty=2)
const rawRead = buildReadHoldingRegisters(1, 0x00, 2);
console.log(rawRead);
// → Uint8Array [0x01, 0x03, 0x00, 0x00, 0x00, 0x02, CRC_LO, CRC_HI]

// Build a “Write Multiple Registers” frame (ID=1, addr=0, values=[10,11])
const rawWrite = buildWriteRegisters(1, 0x00, [0x0A, 0x0B]);
console.log(rawWrite);
// → Uint8Array [0x01, 0x10, 0x00, 0x00, 0x00, 0x02, 0x04, 0x00,0x0A, 0x00,0x0B, CRC_LO, CRC_HI]

[!TIP] Check src/index.ts (or dist/index.js) for all exports

Supported Functions

Modbus Data Functions

The following Modbus-RTU function calls are implemented:

Function Description
readCoils(addr, qty) FC 01 – Read coil status
readDiscreteInputs(addr, qty) FC 02 – Read discrete input status
readHoldingRegisters(addr, qty) FC 03 – Read holding registers
readInputRegisters(addr, qty) FC 04 – Read input registers
writeCoil(addr, state) FC 05 – Write single coil
writeRegister(addr, value) FC 06 – Write single holding register
writeCoils(addr, states) FC 15 – Write multiple coils
writeRegisters(addr, values) FC 16 – Write multiple holding registers
readFileRecord(file, rec, len) FC 20 – Read file record (single ref)
writeFileRecord(file, rec, vals) FC 21 – Write file record (single ref)
maskWriteRegister(addr, and, or) FC 22 – Mask write register
readWriteRegisters(rAddr, rQty, wAddr, vals) FC 23 – Read/write multiple regs
readFifoQueue(addr) FC 24 – Read FIFO queue

[!CAUTION] Not all slave libraries support file records, FIFO queues, mask writes or read-write calls

Auxiliary Client Methods

Utility and configuration methods exposed on ModbusRTU:

Method Purpose
openWebSerial(options) Open a serial port via WebSerial
close() Close the current serial connection
setID(id) Set the Modbus slave ID
getID() Get the current slave ID
setTimeout(ms) Set transaction timeout (ms)
getTimeout() Get current timeout (ms)

Examples

The following demos are fully self‑contained HTML files, served via GitHub Pages:

  • Basic Read/Write Demo Simple page to connect, read two registers, and write two registers.
  • 64‑Register Smoke Test Automated loop testing read/write of 64 registers, coils, and discrete inputs with live counters and error logging.

Current state

  • v0.10: Full modbus data-access coverage
  • v0.9: Full passing tests, smoke test passed, complete README, build scripts in place
  • Beta: Full Modbus RTU function‑code coverage
  • Alpha: Basic structure and layout

Roadmap

  • v1.0.0: Finalize API, apply bug fixes, refine docs, production-ready release

© 2025 Antti Kotajärvi