nodemcu-firmware/docs/modules/gpio.md

GPIO Module

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

This module provides access to the GPIO (General Purpose Input/Output) subsystem.

All access is based on the I/O index number on the NodeMCU dev kits, not the internal GPIO pin. For example, the D0 pin on the dev kit is mapped to the internal GPIO pin 16.

If not using a NodeMCU dev kit, please refer to the below GPIO pin maps for the index↔gpio mapping.

IO index	ESP8266 pin	IO index	ESP8266 pin
0 [*]	GPIO16	7	GPIO13
1	GPIO5	8	GPIO15
2	GPIO4	9	GPIO3
3	GPIO0	10	GPIO1
4	GPIO2	11	GPIO9
5	GPIO14	12	GPIO10
6	GPIO12

** [*] D0(GPIO16) can only be used as gpio read/write. No support for open-drain/interrupt/pwm/i2c/ow. **

gpio.mode()

Initialize pin to GPIO mode, set the pin in/out direction, and optional internal weak pull-up.

Syntax

gpio.mode(pin, mode [, pullup])

Parameters

• pin pin to configure, IO index
• mode one of gpio.OUTPUT, gpio.OPENDRAIN, gpio.INPUT, or gpio.INT (interrupt mode)
• pullup gpio.PULLUP enables the weak pull-up resistor; default is gpio.FLOAT

Returns

nil

Example

gpio.mode(0, gpio.OUTPUT)

See also

• gpio.read()
• gpio.write()

gpio.read()

Read digital GPIO pin value.

Syntax

gpio.read(pin)

Parameters

pin pin to read, IO index

Returns

a number, 0 = low, 1 = high

Example

-- read value of gpio 0.
gpio.read(0)

See also

gpio.mode()

gpio.serout()

Serialize output based on a sequence of delay-times in µs. After each delay, the pin is toggled. After the last cycle and last delay the pin is not toggled.

The function works in two modes:

• synchronous - for sub-50 µs resolution, restricted to max. overall duration,
• asynchrounous - synchronous operation with less granularity but virtually unrestricted duration.

Whether the asynchronous mode is chosen is defined by presence of the callback parameter. If present and is of function type the function goes asynchronous and the callback function is invoked when sequence finishes. If the parameter is numeric the function still goes asynchronous but no callback is invoked when done.

For the asynchronous version, the minimum delay time should not be shorter than 50 μs and maximum delay time is 0x7fffff μs (~8.3 seconds). In this mode the function does not block the stack and returns immediately before the output sequence is finalized. HW timer FRC1_SOURCE mode is used to change the states. As there is only a single hardware timer, there are restrictions on which modules can be used at the same time. An error will be raised if the timer is already in use.

Note that the synchronous variant (no or nil callback parameter) function blocks the stack and as such any use of it must adhere to the SDK guidelines (also explained here). Failure to do so may lead to WiFi issues or outright to crashes/reboots. In short it means that the sum of all delay times multiplied by the number of cycles should not exceed 15 ms.

Syntax

gpio.serout(pin, start_level, delay_times [, cycle_num[, callback]])

Parameters

• pin pin to use, IO index
• start_level level to start on, either gpio.HIGH or gpio.LOW
• delay_times an array of delay times in µs between each toggle of the gpio pin.
• cycle_num an optional number of times to run through the sequence. (default is 1)
• callback an optional callback function or number, if present the function returns immediately and goes asynchronous.

Returns

nil

Example

gpio.mode(1,gpio.OUTPUT,gpio.PULLUP)
gpio.serout(1,1,{30,30,60,60,30,30})  -- serial one byte, b10110010
gpio.serout(1,1,{30,70},8)  -- serial 30% pwm 10k, lasts 8 cycles
gpio.serout(1,1,{3,7},8)  -- serial 30% pwm 100k, lasts 8 cycles
gpio.serout(1,1,{0,0},8)  -- serial 50% pwm as fast as possible, lasts 8 cycles
gpio.serout(1,0,{20,10,10,20,10,10,10,100}) -- sim uart one byte 0x5A at about 100kbps
gpio.serout(1,1,{8,18},8) -- serial 30% pwm 38k, lasts 8 cycles

gpio.serout(1,1,{5000,995000},100, function() print("done") end) -- asynchronous 100 flashes 5 ms long every second with a callback function when done
gpio.serout(1,1,{5000,995000},100, 1) -- asynchronous 100 flashes 5 ms long, no callback

gpio.trig()

Establish or clear a callback function to run on interrupt for a pin.

This function is not available if GPIO_INTERRUPT_ENABLE was undefined at compile time.

Syntax

gpio.trig(pin, [type [, callback_function]])

Parameters

• pin 1-12, pin to trigger on, IO index. Note that pin 0 does not support interrupts.
• type "up", "down", "both", "low", "high", which represent rising edge, falling edge, both edges, low level, and high level trigger modes respectivey. If the type is "none" or omitted then the callback function is removed and the interrupt is disabled.
• callback_function(level) callback function when trigger occurs. The level of the specified pin at the interrupt passed as the parameter to the callback. The previous callback function will be used if the function is omitted.

Returns

nil

Example

do
  -- use pin 1 as the input pulse width counter
  local pin, pulse1, du, now, trig = 1, 0, 0, tmr.now, gpio.trig
  gpio.mode(pin,gpio.INT)
  local function pin1cb(level)
    local pulse2 = now()
    print( level, pulse2 - pulse1 )
    pulse1 = pulse2
    trig(pin, level == gpio.HIGH  and "down" or "up")
  end
  trig(pin, "down", pin1cb)
end

See also

gpio.mode()

gpio.write()

Set digital GPIO pin value.

Syntax

gpio.write(pin, level)

Parameters

• pin pin to write, IO index
• level gpio.HIGH or gpio.LOW

Returns

nil

Example

-- set pin index 1 to GPIO mode, and set the pin to high.
pin=1
gpio.mode(pin, gpio.OUTPUT)
gpio.write(pin, gpio.HIGH)

See also

• gpio.mode()
• gpio.read()