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, 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
```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")
```

## 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.