Raspberry Pi GPIO Expansion - Low Level Peripherals

atomar — Fri, 08 Oct 2021 04:49:32 GMT

Current Revision posted to Documents by atomar on 10/8/2021 4:49:32 AM

Introduction

The Raspberry Pi allows peripherals and expansion boards to access the CPU by exposing the in and outputs. The production board has a 26-pin 2.54mm (100mil) expansion header, arranged in a 2x13 strip. They provide 8 GPIO pins plus access to I2C, SPI, UART), as well as +3V3, +5V and GND supply lines. Pin one is column 0 on the bottom row. Voltage levels are 3v3. There is no over-voltage protection on the board - the intention is that people interested in serious interfacing will use an external board with buffers, level conversion and analog I/O rather than soldering directly onto the main board.

It is also possible to reconfigure some of the pins to provide a second I2C interface. Kernel boot messages go to the UART at 115200bps.

Header Pinout:

Top Row

5V0

DNC

GND

TXD

RXD

GPIO1

DNC

GPIO4

GPIO5

DNC

GPIO6

SPI_CE0_N

SPI_CE1_N

Bottom Row

3V3

SDA0

SCL0

GPIO7

DNC

GPIO0

GPIO2

GPIO3

DNC

SPI_MOSI

SPI_MISO

SPI_SCLK

DNC

Colour legend

+5V

+3.3V

Do not connect

UART

GPIO

SPI

I2C

Power Pins

Maximum permitted current draw from the 3v3 pin is 50mA.

Maximum permitted current draw from the 5v pin is the USB input current (usually 1A) minus any current draw from the rest of the board.

Model A: 1000mA - 500mA -> max power draw: 500mA
Model B: 1000mA - 700mA -> max power draw: 300mA

General Purpose Input/Output (GPIO)

General Purpose Input/Output (GPIO) is a generic pin on a chip whose behaviour (including whether it is an input or output pin) can be controlled (programmed) through software. All the UART, SPI and I2C pins can be reconfigured as GPIO pins, to provide a total of 17 GPIO pins. Each of their functions is detailed in the Broadcom BCM2835 chipset datasheet.

The available alternative functions and their corresponding pins are detailed below. These numbers are in reference to the chipset documentation and may not match the numbers exposed in linux or detailed above. Only fully usable functions are detailed, for some alternative functions not all the necessary pins are available for the functionality to be actually used. All exposed pins can be used for GPIO

Top Row Pinout:

Header	2	4	6	8	10	12	14	16	18	20	22	24	26
Chipset	14	15	18	23	24	25	8	7
Function	5V0	DNC	GND	TXD	RXD	PWM	DNC	GPIO	GPIO	DNC	GPIO	SPI_CE0_N	SPI_CE1_N

Bottom Row Pinout:

Header	1	3	5	7	9	11	13	15	17	19	21	23	25
Chipset	0	1	4	17	21	22	10	9	11
Function	3V3	SDA0	SCL0	GPIO	DNC	GPIO	GPIO	GPIO	DNC	SPI_MOSI	SPI_MISO	SPI_SCLK	DNC

The complete list of chipset pins which are available are:

0, 1, 4, 7, 8, 9, 10, 11, 14, 15, 17, 18, 21, 22, 23, 24, 25

Pin 12 supports PWM.
GPIO voltage level is 3V3 and are not 5V tolerant.
Each GPIO can interrupt, high/low/rise/fall/change.

It is also possible to reconfigure some of the pins to provide an ARM JTAG interface. However ARM_TMS isn't available for this (chipset pin 12 or 27 is needed).

It is also possible to reconfigure some of the pins to provide an I2S (hardware mod may be required) or PCM interface.

MIPI CSI-2

The MIPI CSI-2 interface to a 15-way flat flex connector is Sony sub-LVDS.

DSI

The DSI interface to a 15-way flat flex connector.

CEC

HDMI-CEC (Consumer Electronics Control for HDMI) is supported by hardware but some driver work will be needed and currently isn't exposed into Linux userland.