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.

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.

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.

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

-- 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.

Syntax

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

Parameters

  • id always zero, only one uart supported
  • 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

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 always zero, only one uart supported

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 always 0, only one UART supported
  • data1... string or byte to send via UART

Returns

nil

Example

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