wifi-tally_Oostendam/nodemcu-firmware/docs/modules/softuart.md

SoftUART Module

Since	Origin / Contributor	Maintainer	Source
2019-12-27	pleningerweb, juancgalvez, crasu, galjonsfigur	galjonsfigur	softuart.c

The SoftUART module offers bit-banged serial ports over GPIO pins.

!!! warning

Software implementation of serial port can be unreliable and some reception errors are to be expected.

ESP8266 has only 1 full hardware UART port that is used to program the chip and communicate with NodeMCU firmware. The second port is transmit-only. More information can be found in uart module documentation. This module provides access to more UART ports and can be used to communicate with devices like GSM or GPS modules. The code is based on esp8266-software-uart and Arduino-esp8266-Software-UART projects. Currently doesn't support inverted serial data logic or modes other than 8N1. It's important to notice that this is a software implementation of the serial protocol. There could be some interrupts that make the transmission or reception fail due to invalid timing.

!!! note

SoftUART cannot be used on D0 pin.

softuart.setup()

Creates new SoftUART instance. Note that rx pin cannot be shared between instances but tx pin can.

Syntax

softuart.setup(baudrate, txPin, rxPin)

Parameters

• baudrate: SoftUART baudrate. Maximum supported is 230400.
• txPin: SoftUART tx pin. If set to nil write method will not be supported.
• rxPin: SoftUART rx pin. If set to nil on("data") method will not be supported.

Returns

softuart instance.

Example

-- Create new software UART with baudrate of 9600, D2 as Tx pin and D3 as Rx pin
s = softuart.setup(9600, 2, 3)

SoftUART port

softuart.port:on()

Sets up the callback function to receive data.

Syntax

softuart.port:on(event, trigger, function(data))

Parameters

• event: Event name. Currently only data is supported.
• trigger: Can be a character or a number. If character is set, the callback function will only be run when that character gets received. When a number is set, the callback function will only be run when buffer will have as many characters as number.
• function(data): Callback function. the data parameter is software UART receiving buffer.

Returns

nil

Example

-- Create new software UART with baudrate of 9600, D2 as Tx pin and D3 as Rx pin
s = softuart.setup(9600, 2, 3)
-- Set callback to run when 10 characters show up in the buffer
s:on("data", 10, function(data)
  print("Lua handler called!")
  print(data)
end)

softuart.port:write()

Transmits a byte or sequence of them.

Syntax

softuart.port:write(data)

Parameters

• data: Can be a number or string. When a number is passed, only one byte will be sent. When a string is passed, whole sequence will be transmitted.

Returns

nil

Example

-- Create new software UART with baudrate of 9600, D2 as Tx pin and D3 as Rx pin
s = softuart.setup(9600, 2, 3)
s:write("Hello!")
-- Send character 'a'
s:write(97)