A powerful feature of the Raspberry Pi is the row of GPIO (general-purpose input/output) pins along the top edge of the board.
A 40-pin GPIO header is found on all current Raspberry Pi boards.
Any of the GPIO pins can be designated (in software) as an input or output pin and used for a wide range of purposes. The numbering of the GPIO pins is not in numerical order.
Two 5V pins and two 3V3 pins are present on the board, as well as a number of ground pins (0V), which are unconfigurable.
The remaining pins are all general purpose 3V3 pins, meaning outputs are set to 3V3 and inputs are 3V3-tolerant.
A GPIO pin designated as an output pin can be set to high (3V3) or low (0V).
A GPIO pin designated as an input pin can be read as high (3V3) or low (0V). This is made easier with the use of internal pull-up or pull-down resistors. Pins GPIO2 and GPIO3 have fixed pull-up resistors, but for other pins this can be configured in software.
As well as simple input and output devices, the GPIO pins can be used with a variety of alternative functions, some are available on all pins, others on specific pins.
- PWM (pulse-width modulation)
- Software PWM available on all pins
- Hardware PWM available on GPIO12, GPIO13, GPIO18, GPIO19
- SPI
- SPI0: MOSI (GPIO10); MISO (GPIO9); SCLK (GPIO11); CE0 (GPIO8), CE1 (GPIO7)
- SPI1: MOSI (GPIO20); MISO (GPIO19); SCLK (GPIO21); CE0 (GPIO18); CE1 (GPIO17); CE2 (GPIO16)
- I2C
- Data: (GPIO2); Clock (GPIO3)
- EEPROM Data: (GPIO0); EEPROM Clock (GPIO1)
- Serial
- TX (GPIO14); RX (GPIO15)
A handy reference can be accessed on the Raspberry Pi by opening a terminal window and running the command pinout. This tool is provided by the GPIO Zero Python library, which is installed by default on the Raspberry Pi OS desktop image.
For more details on the advanced capabilities of the GPIO pins see gadgetoid's interactive pinout diagram.
