I2C bus / SPI / 1-Wire

I2C Bus

I2C is a method for communication between sensors, displays, etc. and a microcontroller. I2C is a bus that allows multiple devices to be connected over the same two lines (wires), SDA and SCL. Pullup resistors are required for each bus line, typically 4.7k. Each I2C device on the bus has a 7 bit address, which uniquely identifies it (max 128 addresses). 5V and 3.3V devices may be connected over I2C, provided the pullup resistors are connected to the 3.3V side. I2C level shifter boards are available. The number of nodes is limited by the address space, and by the total bus compacitance of 400 pF, resulting in a communication distance restriction of a few meters (use shielded cable, with shield grounded at one end). You can extend I2c over distances of up to 100 feet using a PCA9615 differential I2C bus extender

Typically specific pins on microcontrollers are allocated for I2C:

I2C	Arduino Uno	Feather M0 Basic	Feather 32u4 Basic	Argon \| Boron
SDA	A4	#20 (SDA)	#2	D0 (SDA)
SCL	A5	#21 (SCL)	#3	D1 (SCL)
SDA1				D2 (D2)
SCL1				D3 (D3)

Adafruit TCA9548A 1-to-8 I2C Multiplexer Breakout product $7/ea

Adafruit TCA9548A 1-to-8 I2C Multiplexer Breakout tutorial

Adafruit ISO1540 Bidirectional I2C Isolator - STEMMA QT / Qwiic

Adafruit List of I2C Addresses

Sparkfun I2C Tutorial

I2C over long wires

SPI

Logic Signals	Master Aliases	Slave Aliases
Serial Clock (SCLK)	SCK/CLK	SCK/CLK
Master Out Slave Input (MOSI)	SDO	SDI
Master Input Slave Output (MISO)	SDI	SDO
Slave Select (SS) / Chip Select (CS)	SS/CS	SS/CS

Multiple slaves can share the SDI, SDO and SCK pins, but each slave must have a unique CS/SS pin. You can typically use any digital I/O pin for Save Select (SS / CS). In most cases, the CS/SS is held high when not in use. Master / slave distance can be extended with the use of transceivers like RS-485.

Arduino SPI reference

Sparkfun tutorial

Adafruit SPI Protocol tutorial

Adafruit SPI tutorial

SPI	Arduino Uno	Feather M4	Feather M0	Feather 32u4 Basic	Argon/Boron
SCLK (SCK/CLK)	#13	#24	#24	#15	D11 (D2)
MOSI	#11	#23	#23	#16	D12 (D3)
MISO	#12	#22	#22	#14	D13 (D20)
SS (CS) [1]	#10	#10	#10	#10 / A10	A5

[1] Each SPI slave must have a unique CS/SS pin.

1-Wire

Uses a 4.7k pullup resistor.

I2S Bus

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