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The GPIO pin will be configured as a digital input. If the voltage of 3.3V is applied to it, the value of input will be 1. If 0V (ground) voltage is applied to it, the value of input will be 0.
Variants DI_UP and DI_DOWN configure the internal pull-up resp. pull-down resistors, so the voltage 3.3V (DI_UP) or ground (DI_DOWN) is connected to the input via the resistor, so even without external voltage applied the input is in a defined state. The DI variant configures the pin so that the pull-up/pull-down resistors are disconnected.
Note: pigpio library supports reading from GPIO pins 0-53.

DO,id

The GPIO pin will be configured as a digital output. If a value of 1 is written to it, the output will be 3.3V. If 0 is written, output voltage will be 0V (ground).
Note: pigpio library supports writing to GPIO pins 0-53.

DO,24

The GPIO pin will be configured as an counter of input events with an optional filter. The counter can register rising signal edges 0V → 3.3V (TRIGGER_UP), falling edges 3.3V → 0V (TRIGGER_DOWN) and arbitrary signal changes (TRIGGER).
Parameter filter is used to set a time filter (in microseconds) to filter the noise (if there is shorter time interval between two events than filter, the second event is ignored).  If not specified, all events are considered.
The value of the I/O tag is equal to the number of registered events, the maximum value being 2^31-1 i.e. 2147483647 and then the counter goes again from 0.
Note: The pigpio library uses a standard input sampling with period of 5 microseconds, i.e. with a frequency of 200 kHz.

TRIGGER,24

TRIGGER,25,1000

The GPIO pin will be configured as PWM (pulse width modulation) output. It is then possible to write values 0-255 controlling the width of pulse from fully off to fully on.
Note: pigpio library supports PWM output for GPIO pins 0-31.

The revision of the hardware (the number from the "Revision" line from the /proc/cpuinfo file. For example, for RPI 3 in this file is the row "Revision        : a02082" and the revision value is 10494082 (after conversion from hexadecimal system).