UART Module

The UART (Universal asynchronous receiver/transmitter) module allows configuration of and communication over the UART serial port.

The default setup for the uart is controlled by build-time settings. The default rate is 115,200 bps. In addition, auto-baudrate detection is enabled for the first two minutes after platform boot. This will cause a switch to the correct baud rate once a few characters are received. Auto-baudrate detection is disabled when uart.setup is called.

!!! important Although there are two UARTs(0 and 1) available to NodeMCU, UART 1 is not capable of receiving data and is therefore transmit only.

uart.alt()

Change UART pin assignment.

Syntax

uart.alt(on)

Parameters

on

• 0 for standard pins
• 1 to use alternate pins GPIO13 and GPIO15

Returns

nil

uart.on()

Sets the callback function to handle UART events.

Currently only the "data" event is supported.

!!! note Due to limitations of the ESP8266, only UART 0 is capable of receiving data.

Syntax

uart.on(method, [number/end_char], [function], [run_input])

Parameters

• method "data", data has been received on the UART
• number/end_char
  • if n=0, will receive every char in buffer
  • if n<255, the callback is called when n chars are received
  • if one char "c", the callback will be called when "c" is encountered, or max n=255 received
• function callback function, event "data" has a callback like this: function(data) end
• run_input 0 or 1. If 0, input from UART will not go into Lua interpreter, and this can accept binary data. If 1, input from UART is treated as a text stream with the DEL, BS, CR and LF characters processed as normal. Completed lines will be passed to the Lua interpreter for execution. Note that the interpreter only processes complete lines.

To unregister the callback, provide only the "data" parameter.

Returns

nil

Example

-- when 4 chars is received.
uart.on("data", 4,
  function(data)
	print("receive from uart:", data)
	if data=="quit" then
	  uart.on("data") -- unregister callback function
	end
end, 0)
-- when '\r' is received.
uart.on("data", "\r",
  function(data)
	print("receive from uart:", data)
	if data=="quit\r" then
	  uart.on("data") -- unregister callback function
	end
end, 0)

uart.setup()

(Re-)configures the communication parameters of the UART.

!!! note

Bytes sent to the UART can get lost if this function re-configures the UART while reception is in progress.

Syntax

uart.setup(id, baud, databits, parity, stopbits[, echo])

Parameters

• id UART id (0 or 1).
• baud one of 300, 600, 1200, 2400, 4800, 9600, 19200, 31250, 38400, 57600, 74880, 115200, 230400, 256000, 460800, 921600, 1843200, 3686400
• databits one of 5, 6, 7, 8
• parity uart.PARITY_NONE, uart.PARITY_ODD, or uart.PARITY_EVEN
• stopbits uart.STOPBITS_1, uart.STOPBITS_1_5, or uart.STOPBITS_2
• echo if 0, disable echo, otherwise enable echo (default if omitted)

Returns

configured baud rate (number)

Example

-- configure for 9600, 8N1, with echo
uart.setup(0, 9600, 8, uart.PARITY_NONE, uart.STOPBITS_1, 1)

uart.getconfig()

Returns the current configuration parameters of the UART.

Syntax

uart.getconfig(id)

Parameters

• id UART id (0 or 1).

Returns

Four values as follows:

• baud one of 300, 600, 1200, 2400, 4800, 9600, 19200, 38400, 57600, 74880, 115200, 230400, 256000, 460800, 921600, 1843200, 3686400
• databits one of 5, 6, 7, 8
• parity uart.PARITY_NONE, uart.PARITY_ODD, or uart.PARITY_EVEN
• stopbits uart.STOPBITS_1, uart.STOPBITS_1_5, or uart.STOPBITS_2

Example

print (uart.getconfig(0))
-- prints 9600 8 0 1   for 9600, 8N1

uart.write()

Write string or byte to the UART.

Syntax

uart.write(id, data1 [, data2, ...])

Parameters

• id UART id (0 or 1).
• data1... string or byte to send via UART

Returns

nil

Example

uart.write(0, "Hello, world\n")

uart.fifodepth()

Report the depth, in bytes, of TX or RX hardware queues associated with the UART.

Syntax

uart.fifodepth(id, dir)

Parameters

• id UART id (0 or 1).
• dir uart.DIR_RX for the RX FIFO, uart.DIR_TX for TX FIFO.

Returns

The number of bytes in the selected FIFO.