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Topic starter 16/08/2025 11:06 pm
Let’s break down the SPI (Serial Peripheral Interface)—a widely used communication protocol in embedded systems and electronics.
🔌 What Is SPI?
SPI (Serial Peripheral Interface) is a high-speed, full-duplex serial communication protocol used to connect microcontrollers to peripherals like sensors, displays, memory chips, and more.
- Developed by Motorola in the 1980s
- Operates in master-slave configuration
- Ideal for short-distance, high-speed communication
🧠 How SPI Works
SPI uses four main signal lines:
| Signal | Description |
|---|---|
| MOSI | Master Out Slave In — data from master to slave |
| MISO | Master In Slave Out — data from slave to master |
| SCLK | Serial Clock — generated by master to sync data |
| SS/CS | Slave Select / Chip Select — enables specific slave device |
🧭 Master-Slave Model
- Master: Controls the clock and initiates communication
- Slave: Responds to master’s commands
- Multiple slaves can be connected, each with its own CS line
🔄 Data Transmission
- SPI is synchronous: data is transferred on clock edges
- Full-duplex: master and slave can send data simultaneously
- Data is typically sent in 8-bit chunks, but other sizes are possible
🛠️ Common Use Cases
| Device Type | Example |
|---|---|
| Flash memory | EEPROM, NOR flash |
| Displays | OLED, TFT LCD |
| Sensors | Accelerometers, temperature sensors |
| SD cards | Storage for microcontrollers |
| DAC/ADC chips | Analog-to-digital or digital-to-analog converters |
⚙️ Advantages of SPI
- Fast: Speeds up to tens of MHz
- Simple: Easy to implement in hardware and software
- Flexible: Supports multiple slaves with individual CS lines
⚠️ Limitations
- No standard protocol: Each device may have its own command set
- No built-in addressing: Requires separate CS lines for each slave
- Short range: Best for PCB-level communication, not long-distance
🧰 Tools & Debugging
- Logic analyzers: Capture and decode SPI signals (e.g., Saleae)
- Bus Pirate / FTDI: Interface with SPI devices from a PC
- Microcontroller libraries: Arduino, STM32 HAL, Raspberry Pi SPI
🔐 Security Implications
SPI interfaces can be exploited for:
- Firmware extraction: Reading flash memory directly
- Data snooping: Monitoring communication between chips
- Device manipulation: Sending rogue commands to peripherals
That’s why SPI lines are often hidden or disabled in production devices.
