SPI vs I2C

SPI is generally faster and better for high-throughput data streaming, while I²C is better for connecting many simple devices using fewer wires.

The choice between them depends on your project’s specific needs for speed, number of connected devices, and available pins on your microcontroller.

Feature	I²C (Inter-Integrated Circuit)	SPI (Serial Peripheral Interface)
Wires Required	2 wires (SDA, SCL) + power/ground	4 wires (MOSI, MISO, SCLK, CS) + power/ground
Max Speed	Slower (typically 100kbps, 400kbps, up to 5Mbps)	Much faster (commonly >10Mbps, up to 100Mbps+)
Data Flow	Half-Duplex (data sends or receives)	Full-Duplex (data sends and receives simultaneously)
Device Addressing	Built-in 7-bit addressing in the protocol	No addressing; uses a dedicated Chip Select (CS) line per device
Hardware Complexity	More complex protocol, but simpler wiring	Simpler protocol, but more complex wiring for multiple devices
Key Advantage	Uses very few pins to connect many devices	Raw speed and simplicity of data transfer

I²C (Inter-Integrated Circuit) 🧯

I²C uses a shared bus, meaning multiple devices can be connected to the same two pins on your microcontroller.

Fewer Wires: Only needs two wires (SDA for data and SCL for clock), regardless of how many devices are on the bus. This is a huge advantage when you are low on available pins.
Built-in Addressing: Each device has a unique address. The master device selects which device it wants to talk to by sending its address first.
Acknowledgement System: The protocol includes acknowledgement (ACK) and negative-acknowledgement (NACK) bits, confirming that data was received correctly. This makes it inherently more reliable.
Multi-Master Support: The I²C standard allows for multiple master devices on the same bus, though this is complex and less commonly used in simple projects.

Slower Speed: The protocol overhead from start/stop bits, addressing, and acknowledgement bits makes it significantly slower than SPI.
Half-Duplex: Data can only travel in one direction at a time on the single data line.
More Complex Protocol: The master device has to manage addresses, check for acknowledgements, and handle bus states, making the underlying driver logic more complex.

SPI uses a master-slave architecture where the master controls communication with one or more slave devices.

High Speed: SPI is extremely fast because there’s very little protocol overhead. It’s essentially a direct stream of bits, making it ideal for high-throughput applications like displays, SD cards, and some ADCs.
Full-Duplex: With separate lines for sending (MOSI - Master Out Slave In) and receiving (MISO - Master In Slave Out), data can be sent and received at the same time.
Simple Protocol: The protocol itself is very simple. The master pulls a device’s Chip Select line low and starts sending clock pulses and data. There’s no addressing or acknowledgement to manage.

More Wires: It requires at least four wires for a single device.
Complex Wiring for Multiple Devices: Each additional slave device requires its own dedicated Chip Select (CS) line from the master. Connecting five SPI devices would require nine pins (MOSI, MISO, SCLK, and five CS lines), which can quickly consume all the available pins on a microcontroller.
No Acknowledgement: There is no built-in confirmation that a slave device received the data, so the master has to assume the communication was successful.
Single Master Only: The standard protocol does not support multiple master devices.