UART

UART implements the standard UART/USART duplex serial communications protocol. At the physical level it consists of 2 lines: RX and TX. The unit of communication is a character (not to be confused with a string character) which can be 8 or 9 bits wide.

UiFlow2 Example

Echo

Open the cores3_echo_exmaple.m5f2 project in UiFlow2.

This example demonstrates how to utilize UART interfaces by echoing back to the sender any data received on configured UART.

UiFlow2 Code Block:

Example output:

None

MicroPython Example

Echo

This example demonstrates how to utilize UART interfaces by echoing back to the sender any data received on configured UART.

MicroPython Code Block:

# SPDX-FileCopyrightText: 2024 M5Stack Technology CO LTD
#
# SPDX-License-Identifier: MIT

import os, sys, io
import M5
from M5 import *
from hardware import UART
import time


label0 = None
uart1 = None


i = None


def setup():
    global label0, uart1, i

    M5.begin()
    Widgets.fillScreen(0x222222)
    label0 = Widgets.Label("label0", 102, 85, 1.0, 0xFFFFFF, 0x222222, Widgets.FONTS.DejaVu18)

    uart1 = UART(1, baudrate=115200, bits=8, parity=None, stop=1, tx=9, rx=10)
    i = 0


def loop():
    global label0, uart1, i
    M5.update()
    uart1.write(i)
    if uart1.any():
        label0.setText(str(uart1.read()))
    i = (i if isinstance(i, (int, float)) else 0) + 1
    time.sleep(1)


if __name__ == "__main__":
    try:
        setup()
        while True:
            loop()
    except (Exception, KeyboardInterrupt) as e:
        try:
            from utility import print_error_msg

            print_error_msg(e)
        except ImportError:
            print("please update to latest firmware")

Example output:

None

API

class UART

class UART(id, baudrate=9600, bits=8, parity=None, stop=1, *, ...)

Construct a UART object of the given id.

For more parameters, please refer to init.

UiFlow2 Code Block:

MicroPython Code Block:

from hadrware import UART

uart1 = UART(1, baudrate=115200, bits=8, parity=None, stop=1, tx=9, rx=10)

init(baudrate=9600, bits=8, parity=None, stop=1, *, ...)

Initialise the UART bus with the given parameters.

Parameters:

baudrate (int) – the clock rate.
bits (int) – the number of bits per character, 7, 8 or 9.
parity (None or int) – the parity, None, 0 (even) or 1 (odd).
stop (int) – the number of stop bits, 1 or 2.

Keyword Arguments:

tx – the TX pin to use.
rx – the RX pin to use.
rts – the RTS (output) pin to use for hardware receive flow control.
cts – the CTS (input) pin to use for hardware transmit flow control.
txbuf (int) – the length in characters of the TX buffer.
rxbuf (int) – the length in characters of the RX buffer.
timeout (int) – the time to wait for the first character (in ms).
timeout_char (int) – the time to wait between characters (in ms).
invert (int) –
which lines to invert.
- 0 will not invert lines (idle state of both lines is logic high).
- UART.INV_TX will invert TX line (idle state of TX line now logic low).
- UART.INV_RX will invert RX line (idle state of RX line now logic low).
- UART.INV_TX | UART.INV_RX will invert both lines (idle state at logic low).
flow (int) –
which hardware flow control signals to use. The value is a bitmask.
- 0 will ignore hardware flow control signals.
- UART.RTS will enable receive flow control by using the RTS output pin to signal if the receive FIFO has sufficient space to accept more data.
- UART.CTS will enable transmit flow control by pausing transmission when the CTS input pin signals that the receiver is running low on buffer space.
- UART.RTS | UART.CTS will enable both, for full hardware flow control.
mode (int) –
the mode of the UART. The value is a bitmask.
- UART.MODE_UART specifies regular UART mode.
- UART.MODE_RS485_HALF_DUPLEX specifies half duplex RS485 UART mode control by RTS pin.
- UART.MODE_IRDA specifies IRDA UART mode.
- UART.MODE_RS485_COLLISION_DETECT specifies RS485 collision detection UART mode (used for test purposes).
- UART.MODE_RS485_APP_CTRL specifies application control RS485 UART mode (used for test purposes).

Note

It is possible to call init() multiple times on the same object in order to reconfigure UART on the fly. That allows using single UART peripheral to serve different devices attached to different GPIO pins. Only one device can be served at a time in that case. Also do not call deinit() as it will prevent calling init() again.

UiFlow2 Code Block:

MicroPython Code Block:

uart1.init(baudrate=115200, bits=8, parity=None, stop=1, tx=9, rx=10)

deinit()

Turn off the UART bus.

Note

You will not be able to call init() on the object after deinit(). A new instance needs to be created in that case.

UiFlow2 Code Block:

MicroPython Code Block:

uart1.deinit()

any()

Returns an integer counting the number of characters that can be read without blocking. It will return 0 if there are no characters available and a positive number if there are characters. The method may return 1 even if there is more than one character available for reading.

Returns:: the number of characters available for reading.
Return type:: int

For more sophisticated querying of available characters use select.poll:

poll = select.poll()
poll.register(uart, select.POLLIN)
poll.poll(timeout)

UiFlow2 Code Block:

MicroPython Code Block:

print(uart1.any())

read([nbytes])

Read characters. If nbytes is specified then read at most that many bytes, otherwise read as much data as possible. It may return sooner if a timeout is reached. The timeout is configurable in the constructor.

Returns:: a bytes object containing the bytes read in. Returns None on timeout.
Return type:: bytes or None

UiFlow2 Code Block:

MicroPython Code Block:

print(uart1.read())

readinto(buf[, nbytes])

Read bytes into the buf. If nbytes is specified then read at most that many bytes. Otherwise, read at most len(buf) bytes. It may return sooner if a timeout is reached. The timeout is configurable in the constructor.

Returns:: number of bytes read and stored into buf or None on timeout.
Return type:: int or None

UiFlow2 Code Block:

MicroPython Code Block:

buf = bytearray(10)
uart1.readinto(buf)

readline()

Read a line, ending in a newline character. It may return sooner if a timeout is reached. The timeout is configurable in the constructor.

Returns:: the line read or None on timeout.
Return type:: str or None

UiFlow2 Code Block:

MicroPython Code Block:

print(uart1.readline())

write(buf)

Write the buffer of bytes to the bus.

Parameters:: buf (bytes or bytearray or str) – the buffer of bytes to write.
Returns:: number of bytes written or None on timeout.
Return type:: int or None

UiFlow2 Code Block:

MicroPython Code Block:

uart1.write('1234!')

sendbreak()

Send a break condition on the bus. This drives the bus low for a duration longer than required for a normal transmission of a character.

UiFlow2 Code Block:

MicroPython Code Block:

uart1.sendbreak()

flush()

Waits until all data has been sent. In case of a timeout, an exception is raised. The timeout duration depends on the tx buffer size and the baud rate. Unless flow control is enabled, a timeout should not occur.

Note

For the rp2, esp8266 and nrf ports the call returns while the last byte is sent. If required, a one character wait time has to be added in the calling script.

UiFlow2 Code Block:

MicroPython Code Block:

uart1.flush()

txdone()

Tells whether all data has been sent or no data transfer is happening. In this case, it returns True. If a data transmission is ongoing it returns False.

Note

For the rp2, esp8266 and nrf ports the call may return True even if the last byte of a transfer is still being sent. If required, a one character wait time has to be added in the calling script.

UiFlow2 Code Block:

MicroPython Code Block:

print(uart1.txdone())

irq(handler=None, trigger=0, hard=False)

Configure an interrupt handler to be called when a UART event occurs.

Parameters:

handler (func) – an optional function to be called when the interrupt event triggers. The handler must take exactly one argument which is the UART instance.
trigger (int) –
configures the event(s) which can generate an interrupt. Possible values are a mask of one or more of the following:
- UART.IRQ_RXIDLE interrupt after receiving at least one character and then the RX line goes idle.
- UART.IRQ_RX interrupt after each received character.
- UART.IRQ_TXIDLE interrupt after or while the last character(s) of a message are or have been sent.
- UART.IRQ_BREAK interrupt when a break state is detected at RX
hard (bool) – if true a hardware interrupt is used. This reduces the delay between the pin change and the handler being called. Hard interrupt handlers may not allocate memory; see Writing interrupt handlers.

Returns:

Returns an irq object.

Due to limitations of the hardware not all trigger events are available on all ports.

Availability of triggers
Port / Trigger	IRQ_RXIDLE	IRQ_RX	IRQ_TXIDLE	IRQ_BREAK
CC3200		yes
ESP32	yes	yes		yes
MIMXRT	yes		yes
NRF		yes	yes
RENESAS-RA	yes	yes
RP2	yes		yes	yes
SAMD	yes	yes	yes
STM32	yes	yes

Note

The ESP32 port does not support the option hard=True.
The rp2 port’s UART.IRQ_TXIDLE is only triggered when the message is longer than 5 characters and the trigger happens when still 5 characters are to be sent.
The rp2 port’s UART.IRQ_BREAK needs receiving valid characters for triggering again.
The SAMD port’s UART.IRQ_TXIDLE is triggered while the last character is sent.
On STM32F4xx MCU’s, using the trigger UART.IRQ_RXIDLE the handler will be called once after the first character and then after the end of the message, when the line is idle.

Availability: cc3200, esp32, mimxrt, nrf, renesas-ra, rp2, samd, stm32.

RTS

CTS: Flow control options.

MODE_UART

MODE_RS485_HALF_DUPLEX

MODE_IRDA

MODE_RS485_COLLISION_DETECT

MODE_RS485_APP_CTRL: UART mode options.

IRQ_RXIDLE

IRQ_RX

IRQ_TXIDLE

IRQ_BREAK: IRQ trigger sources.