Web Serial Polyfill

A Web Serial API implementation over WebUSB for USB-to-serial adapters. Useful on platforms like Android that support WebUSB but not Web Serial.

Fork of google/web-serial-polyfill with added support for PL2303 and FTDI chips.

Supported hardware

| Chip family | Class | Examples | |---|---|---| | CDC-ACM | Standard USB serial | Arduino, STM32, RP2040, CP210x (some) | | Prolific PL2303 | Vendor (incl. HXN/G-series) | PL2303, PL2303HX, PL2303GC/GB/GT/GL/GE/GS | | FTDI | Vendor | FT232R, FT232H, FT2232H, FT4232H, FT230X/FT231X, FT233HP/FT232HP |

Chip type is auto-detected from the USB vendor/product ID. No configuration required.

Install

npm install @cmuav/web-serial-polyfill

Usage

import { serial } from '@cmuav/web-serial-polyfill';

// Prompt user to pick a USB device
const port = await serial.requestPort();
await port.open({ baudRate: 115200 });

// Read
const reader = port.readable!.getReader();
const { value } = await reader.read();
reader.releaseLock();

// Write
const writer = port.writable!.getWriter();
await writer.write(new Uint8Array([0x01, 0x02]));
writer.releaseLock();

await port.close();

FTDI details

The FTDI driver handles:

• Chip detection via bcdDevice — SIO, FT232A/B/R, FT2232C/H, FT4232H, FT232H, FTX, and HP-series
• Baud rate divisor encoding — 232BM algorithm (48 MHz) for standard chips, 2232H algorithm (120 MHz) for hi-speed chips
• Status byte stripping — FTDI prepends 2 bytes (modem + line status) per USB packet; these are automatically removed from the readable stream
• Multi-channel — correct wIndex channel encoding for FT2232/FT4232 multi-port devices

Development

npm install
npm run build

License

Apache-2.0