Microcontrollers with SPI

What is SPI?

SPI (Serial Peripheral Interface) is a high-speed, full-duplex communication protocol used in embedded systems. Developed by Motorola, it is widely used to connect microcontrollers with peripherals such as sensors, memory devices, and displays.

Key Features of SPI

• Full-Duplex Communication: Transmit and receive data simultaneously.
• High-Speed Data Transfer: Operates faster than I²C, making it ideal for high-speed applications.
• Four-Wire Interface: Uses MOSI (Master Out Slave In), MISO (Master In Slave Out), SCLK (Clock), and SS/CS (Slave Select).
• Master-Slave Architecture: One master controls multiple slave devices.
• Low Protocol Overhead: Simple communication without start/stop bits.

Microcontrollers with Built-in SPI

Most modern microcontrollers support SPI natively. Popular options include:

• Arduino (e.g., Uno, Nano): SPI is available on pins 11 (MOSI), 12 (MISO), 13 (SCK), and 10 (SS).
• ESP32/ESP8266: Supports SPI on multiple configurable pins.
• STM32 Series: Offers advanced SPI peripherals with DMA support.
• Raspberry Pi Pico: Provides up to two SPI controllers for flexible interfacing.
• AVR Microcontrollers: Integrated SPI modules in Atmel AVR series.

How to Set Up SPI Communication

To use SPI, connect all devices to the shared lines and assign unique chip select pins for each slave. Below are the steps:

Basic Steps:

1. Connect the SCLK, MOSI, and MISO lines of all devices.
2. Connect the CS/SS pin of each slave to a unique GPIO pin on the master.
3. Configure the master and slave devices for the same clock polarity (CPOL) and clock phase (CPHA).
4. Initialize SPI in the microcontroller's code.
5. Activate the slave by pulling its CS/SS pin low during communication.

Example Code: SPI Communication

Using Arduino as SPI Master

// Example SPI communication using Arduino as Master
#include 

void setup() {
    SPI.begin(); // Initialize SPI
    Serial.begin(9600);
    Serial.println("SPI Master Initialized");
    pinMode(10, OUTPUT); // CS pin
}

void loop() {
    digitalWrite(10, LOW); // Activate slave
    SPI.transfer(0x42);    // Send data to slave
    digitalWrite(10, HIGH); // Deactivate slave
    delay(1000);
}
            

Using Arduino as SPI Slave

// Example SPI communication using Arduino as Slave
#include 

volatile byte receivedData;

void setup() {
    SPI.begin();           // Initialize SPI
    pinMode(MISO, OUTPUT); // Configure MISO as output
    SPCR |= _BV(SPE);      // Enable SPI in slave mode
    Serial.begin(9600);
}

ISR(SPI_STC_vect) {
    receivedData = SPDR;   // Read data from SPI data register
    Serial.print("Received: ");
    Serial.println(receivedData, HEX);
}

void loop() {
    // Main loop remains empty
}
            

Troubleshooting SPI

Common issues and their solutions:

• Data Corruption: Ensure clock polarity (CPOL) and phase (CPHA) match between master and slave.
• No Communication: Verify proper connections and that the slave's CS pin is pulled low.
• Shared Bus Interference: Avoid simultaneous activation of multiple slaves.

Example Projects with SPI

Project 1: SPI SD Card Reader

Use SPI to interface with an SD card module for reading and writing data.

Project 2: TFT Display Control

Use SPI to send graphical data to an SPI-based TFT display module.

Further Reading

For more information about SPI, check out:

• SPI Protocol Demystified - A detailed guide.
• Practical SPI for Engineers - A practical tutorial.

Conclusion

SPI is an efficient and high-speed protocol for interfacing microcontrollers with peripherals. Its flexibility and low overhead make it a go-to choice for embedded systems requiring fast communication.