UART, SPI, and I2C are all serial communication protocols used to connect microcontrollers to peripherals. SPI is fastest (high-speed display/SD cards) but uses 4+ wires. I2C uses 2 wires, supporting multiple master/slave devices (sensors/EEPROMs). UART is a simple 2-wire, asynchronous point-to-point protocol often used for debug consoles.
Key Differences at a Glance
| Feature | UART (Asynchronous) | I2C (Synchronous) | SPI (Synchronous) |
|---|---|---|---|
| Speed | Slow (< 1Mbps) | Moderate (100 kbps - 3.4 Mbps) | High (> 50 Mbps) |
| Wires | 2 (TX, RX) + GND | 2 (SDA, SCL) + GND | 4 (MOSI, MISO, SCK, CS) + GND |
| Distance | Long | Short (on-board) | Very Short (on-board) |
| Devices | Point-to-Point (1-to-1) | Multi-Master/Multi-Slave | Single-Master/Multi-Slave |
| Hardware | Simple (no clock) | Moderate (pull-up resistors) | Complex (4 wires/slave) |
Detailed Breakdown
UART (Universal Asynchronous Receiver-Transmitter):
- Pros: Simplest to implement, requires only two wires (TX and RX), asynchronous (no clock line).
- Cons: Slower than SPI/I2C, usually limited to one-to-one communication.
- Best Use: Serial port debugging, GPS modules, Bluetooth modules.
I2C (Inter-Integrated Circuit):
- Pros: Supports multiple masters and multiple slaves on just two wires (SDA, SDL), making it ideal for large sensor networks.
- Cons: Slower than SPI, higher power consumption (pull-up resistors), more complex protocol.
- Best Use: Connecting multiple low-speed sensors, EEPROMs, OLED displays, and IoT sensors.
SPI (Serial Peripheral Interface):
- Pros: High-speed, full-duplex (simultaneous data transfer), no addressing needed.
- Cons: Requires more pins (4+), no built-in flow control, requires a dedicated chip select (CS) line for each slave.
- Best Use: SD cards, fast high-resolution TFT displays, Ethernet controllers, external memory.