Since HAA V12 Merlin, GPIOs behavior must be configured in an array to determine how hardware will work.

This array is declared by the key "io":[...] and contains other arrays. Each other array is a group of GPIOs declaration.

By default, GPIOs are disabled, but they must be configured as INPUT, OUTPUT, OPEN-DRAIN... with different options, like pull-up resistors, modes, PWM...

Structure of "io":[...] array is:

"io" : [ 
  [ [ gpio 1, gpio 2, gpio N, ...], mode, pull-up/down, options... ], 
  [ [ gpio 1, gpio 2, gpio N, ...], mode, pull-up/down, options... ], 
  [ [ gpio 1, gpio 2, gpio N, ...], mode, pull-up/down, options... ], 
  ...
]

• [ gpio 1, gpio 2, gpio N, ...] is a GPIO array, according to hardware. All GPIO numbers into this array will have same configuration as follow.
• mode is the main operation mode for these [ gpios ].

Depending of selected mode, different options are available.

ADC pin of ESP8266 doesn't need any declaration here.

- Options with * are available only for ESP32 models. They are incompatible with ESP8266 models.

Depending on the hardware attached to a GPIO there may be a need for enabling an internal pull-up or pull-down resistor.

** Glitch filter is only available for ESP32-C and ESP32-S. They feature hardware filters to remove unwanted glitch pulses from the INPUT GPIO, which can help reduce false triggering of the interrupt and prevent a noise being routed to the peripheral side. Each GPIO can be configured with a glitch filter, which can be used to filter out pulses shorter than two sample clock cycles.

[ [ gpios ], mode, pull-up/down ]

Used to set a GPIO disable. This sets GPIO in a high impedance state without any function.

In ESP32 chips, disabled GPIOs must be declared explicitly.

[ [ gpios ], mode, pull-up/down ]

Used to set a GPIO as input, needed for some drivers. This mode is not the proper to use with buttons, switches, or any other binary sensor. For those, use mode 6.

In ESP8266, all user GPIOs (except 9 an 10) are set as INPUT at boot because disabling them can cause some hardware issues.

[ [ gpios ], mode, pull-up/down, initial value ]

If expansion interfaces are used, remember to use hundreds to select expander of GPIO. For example, GPIO 6 of first I/O Expander will be 106.

[ [ gpios ], mode, pull-up/down, button mode, button filter, max us pulse duration ]

With some peripherals and hardware the actual GPIO signal may need to be inverted to ensure the correct action is performed when the GPIO changes state. This is normal for binary inputs that are active low.

Other peripherals send a pulse instead setting GPIO signal high constantly. For example, an AC@50Hz signal from mains, that will do GPIO signal to trigger low and high 50 times per second. In this cases, input with pulse detection is needed.

The button filter can be set to any integer value between 1 (soft) and 255 (hard) to avoid interference such as debounce from the input when a button pressed.

Note: pulse detection, inputs from MCP23017 and GPIOs without ISR (hardware interruption), like GPIO 16 from ESP8266, need Binary Input Continuous Mode enabled with "c":1 key into General Configuration.

max us pulse duration: Maximum pulse duration in us (microseconds) in pulse mode. If pulse duration is higher, it will be treat like LOW GPIO state or not pulse.

[ [ gpios ], mode, pull-up/down, initial value, PWM mode, PWM dithering ]

By default, trailing mode is used. But some hardware may require to use leading, like TRIACs. This array will specify which channels must be leading:

[ [ gpios ], mode, pull-up/down, initial value, PWM mode, timer ]

By default, trailing mode is used. But some hardware may require to use leading, like TRIACs. This array will specify which channels must be leading:

Configure GPIOs to use as ADC Inputs. It has a 12 bits width, getting raw values from 0 to 4095.

Check which GPIOs are ADC available, because only ADC unit 1 is supported. ADC unit 2 from some ESP32 chips can not be used because it is attached to WiFi and both are self-exclusive.

ESP8266 has only one ADC pin with 10 bits width (0 to 1023) and it doesn't need any configuration.

[ [ gpios ], mode, pull-up/down, attenuation ]