nodemcu-firmware/docs/modules/uart.md

UART Module

Since	Origin / Contributor	Maintainer	Source
2014-12-22	Zeroday	Zeroday	uart.c

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

If the UART is in use as the system console, it is unavailable for use by this module. Instead, refer to the console module.

Before using a UART, you must call uart.setup and uart.start to set them up.

uart.on()

Sets the callback function to handle UART events. For a UART used by the console, refer to the console module instead.

Syntax

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

Parameters

• id uart id, except console uart. Default value is uart 0.
• method "data", data has been received on the UART. "error", error occurred on the UART.
• number/end_char. Only for event data.
  • if pass in a number n, the callback will called when n chars are received.
  • if n=0, will receive every char in buffer.
  • if pass in a one char string "c", the callback will called when "c" is encounterd, or max n=255 received.
• function callback function.
  • event "data" has a callback like this: function(data) end
  • event "error" has a callback like this: function(err) end. err could be one of "out_of_memory", "break", "rx_error".

To unregister the callback, provide only the "method" 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)
-- 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)

-- uart 2
uart.on(2, "data", "\r",
  function(data)
	print("receive from uart:", data)
  end)
  
-- error handler
uart.on(2, "error",
  function(data)
	print("error from uart:", data)
  end)

uart.setup()

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

Syntax

uart.setup(id, baud, databits, parity, stopbits, pins)

Parameters

• id uart id, except console uart
• 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
• pins
  • table with the following entries:
    • tx int. TX pin. Required
    • rx int. RX pin. Required
    • cts in. CTS pin. Optional
    • rts in. RTS pin. Optional
    • tx_inverse boolean. Inverse TX pin. Default: false
    • rx_inverse boolean. Inverse RX pin. Default: false
    • cts_inverse boolean. Inverse CTS pin. Default: false
    • rts_inverse boolean. Inverse RTS pin. Default: false
    • flow_control int. Combination of uart.FLOWCTRL_NONE, uart.FLOWCTRL_CTS, uart.FLOWCTRL_RTS. Default: uart.FLOWCTRL_NONE

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.setup(2, 115200, 8, uart.PARITY_NONE, uart.STOPBITS_1, {tx = 17, rx = 16})

uart.getconfig()

Returns the current configuration parameters of the UART.

Syntax

uart.getconfig(id)

Parameters

• id uart id, except console uart

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.start()

Start the UART.

Syntax

uart.start(id)

Parameters

• id uart id, except console uart

Returns

Boolean. true if uart is started.

uart.stop()

Stop the UART.

Syntax

uart.stop(id)

Parameters

• id uart id, except console uart

Returns

nil

uart.setmode()

Set UART controllers communication mode

Syntax

uart.setmode(id, mode)

Parameters

• id uart id, except console uart
• mode value should be one of
  • uart.MODE_UART default UART mode, is set after uart.setup() call
  • uart.MODE_RS485_COLLISION_DETECT receiver must be always enabled, transmitter is automatically switched using RTS pin, collision is detected by UART hardware (note: no event is generated on collision, limitation of esp-idf)
  • uart.MODE_RS485_APP_CONTROL receiver/transmitter control is left to the application
  • uart.MODE_RS485_HALF_DUPLEX receiver/transmitter are controlled by RTS pin
  • uart.MODE_IRDA

Returns

nil

uart.txflush()

Wait for any data currently in the UART transmit buffers to be written out. It can be useful to call this immediately before a call to node.sleep() because otherwise data might not get written until after wakeup.

Syntax

uart.txflush(id)

Parameters

• id uart id, except console uart

Returns

nil

Example

uart.write(0, "I want this to show up now not in 5 seconds")
uart.txflush(0)
node.sleep({secs=5})

See also

node.sleep()

uart.wakeup()

Configure the light sleep wakeup threshold. This is the number of positive edges that must be seen on the UART RX pin before a light sleep wakeup will be triggered. The minimum value is 3. The default value is undefined, therefore you should always call this function before the first time you call node.sleep() with the uart option set.

Syntax

uart.wakeup(id, val)

Parameters

• id uart id, except console uart
• val the new value

Returns

nil

Example

uart.wakeup(0, 5)

See also

node.sleep()

uart.write()

Write string or byte to the UART.

Syntax

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

Parameters

• id uart id, except console uart
• data1... string or byte to send via UART

Returns

nil

Example

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