Scientific Specialties

Date: 3 Apr 2020 Raspberry Pi OS: Raspbian Hardware: Raspberry Pi 4 Description: GPIO Numbering/Pinout

The Raspberry Pi has two common pin numbering systems, commonly called pinouts. Some pins are dedicated for certain functions for I2C, SPI, while others are able to perform general input/output. The lines become blurry as the general pins can be programmed to operate like the specialize pins. This makes the Raspberry Pi such a diverse, and sometimes complicated piece of electronic hardware that it can perform many functions.

Raspberry Pi Pinout

Importance of the types and functions of these pins are important for the longevity of the motherboards as-well-as the health and safety of the circuits themselves.

The first 26 pins are the same as the GPIO pins for the original Raspberry pi Model A and Model B boards. Raspberry Pi Model A+, Model B+, and Model B2 have 40-pin GPIO pins and the above diagram shows the

There are three different power pins, which are Pins #1, #2, and #4. Pin #1 is 3.3 volts, while Pins #2 and #4 are 5.0 volts. It is important that power for each circuit be carefully designed for each application and circuit.

Colours above are designated for their function.

Red	Power
Black	Ground
Yellow	UART
Green	GPIO
Purple	SPI
Dark Blue	I2C

3.3 volt power: The typical milliamp draw from both Pin #1 and Pin #17 is 50 milliamps maximum.

Pins #3 and #5 are used for the I2C interface, where many different peripherals can be connected to these two pins to communicate data back and forth and the data is kept neatly separate. The acronym SDA is for Serial Data and SCL is for Serial Clock, and I2C means Inter-Integrated Circuit. Serial Data is the line where the data is sent and received, where the Serial Clock is the line that carries the clock signal so that data is timed according to this clock.

I2C has two wires, with four speeds:

Standard Mode	100 kbps
Fast Mode	400 kbps
High Speed Mode	3.4 Mbps
Ultra Fast Mode	5 Mbps

Data is synchronous, and can have an unlimited number of masters, while has a maximum number of 1008 of slaves, which is lots.

Pin #7 is the GPIO General Clock (GCLK) that can be set to create a square wave up to 125 MHz at 1.2 volts. Pins with the GEN suffix are common pins that can be used for general input or output purposes, which are Pins #11, #12, #13, #15, #16, #18, and #22.

UART communication is with Pin #8 and Pin #10. Pin #8 is abbreviated as TXD0, or the transmit asynchronous data, and Pin #10 is to receive asynchronous data. This communication type is slightly different as a clock signal is not needed to send and receive data. Remember taht the UART pins in BCM mode are GPIO #14 and GPOP#15. UART is the abbreviation for Universal Asynchronous Receiver/Transmitter.

Serial Peripheral Interface (SPI) pins are #19, #21, #23, #24, #26, #35, #36, #38, and #40. Abbreviations are SCLK for Serial Clock, CE is Chip Enable or Chip Select, MOSI is Master Out Slave In, MISO is Master In Slave Out, and on the odd occasion there is MOMI which is Master Out Master In for a single wire used for data.

There are many interesting and fascinating projects that can be created with these pins on the Raspberry Pi. What things do you want to make?