nodemcu-firmware/docs/modules/uart.md

# UART Module
| Since  | Origin / Contributor  | Maintainer  | Source  |
| :----- | :-------------------- | :---------- | :------ |
| 2014-12-22 | [Zeroday](https://github.com/funshine) | [Zeroday](https://github.com/funshine) | [uart.c](../../app/modules/uart.c)|

The [UART](https://en.wikipedia.org/wiki/Universal_asynchronous_receiver/transmitter) (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, can accept binary data. If 1, input from UART will go into Lua interpreter, and run.

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

#### Returns
`nil`

#### Example
```lua
-- 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
```lua
-- 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
```lua
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
```lua
uart.write(0, "Hello, world\n")
```