UART

Send and receive serial data over UARTUniversal Asynchronous Receiver-Transmitter. This example uses a loopback wiring (TXTransmit connected to RXReceive) to verify that data written on one pin is read back on the other. See the uart APIApplication Programming Interface reference for the full type surface.

Hardware

• Any ESP32 board with two available GPIOGeneral-Purpose Input/Output pins
• One jumper wire connecting TXTransmit to RXReceive
• USBUniversal Serial Bus cable

Code

import {sleep} from 'mikro/sleep'
import {Uart} from 'mikro/uart'

// UART loopback: connect TX (GPIO 16) to RX (GPIO 17) with a jumper wire
const TX_PIN = 16
const RX_PIN = 17
await sleep(2000)
const uart = Uart(1, {tx: TX_PIN, rx: RX_PIN, baudRate: 115200}).orPanic('Failed to start UART')

const message = new TextEncoder().encode('Hello from UART!\n')
uart.write(message).orPanic('Failed to write')

const reader = uart.read()

if (!reader.ok) {
  console.error('Failed to start reading:', reader.error)
} else {
  // Give data a moment to loop back
  await sleep(1000)
  for await (const chunk of reader.value) {
    if (!chunk.ok) {
      console.error('UART read error:', chunk.error)
      break
    }
    console.log('Received: %s', new TextDecoder().decode(chunk.value))
  }
}

uart.end()
console.log('Done!')

Walkthrough

1. UARTUniversal Asynchronous Receiver-Transmitter instance. Uart(port, options) claims the pins, installs the driver and returns a Result with the handle. Port 1 is used here (port 0 is typically reserved for the USBUniversal Serial Bus console). The baudRate must match between sender and receiver.

2. Lifecycle. .orPanic() on the factory's Result gives a clear crash message if the port cannot start. uart.end() releases the port.

3. Writing. uart.write() sends a Uint8Array. Use TextEncoder to convert strings to bytes.

4. Reading. uart.read() returns an async iterator that yields Result<Uint8Array, UartError> items. Check .ok before reading .value; a non-ok chunk reports a read failure. The iterator completes when uart.end() is called. Use TextDecoder to convert bytes back to strings.

5. Loopback test. With TXTransmit wired to RXReceive, the message you send is immediately received. This is a simple way to verify UARTUniversal Asynchronous Receiver-Transmitter works before connecting to an actual peripheral.

Create project

pnpm

pnpm create mikro --template uart

npm

npm create mikro -- --template uart

yarn

yarn create mikro --template uart

bun

bun create mikro --template uart

Run it

pnpm

pnpm install
pnpm mikro flash  # only needed once per board
pnpm mikro dev

npm

npm install
npx mikro flash  # only needed once per board
npx mikro dev

yarn

yarn install
yarn mikro flash  # only needed once per board
yarn mikro dev

bun

bun install
bunx mikro flash  # only needed once per board
bunx mikro dev

The console output shows "Hello from UARTUniversal Asynchronous Receiver-Transmitter!" echoed back.

View source on GitHub