How to Use SPI in Arduino: Simple Guide with Example

To use SPI in Arduino, include the SPI.h library, initialize SPI with SPI.begin(), and communicate using functions like SPI.transfer(). This allows your Arduino to talk to SPI devices like sensors or displays using the SPI protocol.

Syntax

Here is the basic syntax to use SPI in Arduino:

• #include <SPI.h>: Includes the SPI library.
• SPI.begin(): Initializes the SPI bus.
• SPI.transfer(data): Sends and receives a byte over SPI.
• pinMode(SS, OUTPUT): Sets the Slave Select pin as output to control device selection.

You control the Slave Select (SS) pin manually to start and stop communication with the SPI device.

arduino

#include <SPI.h>

void setup() {
  pinMode(SS, OUTPUT); // Set Slave Select pin as output
  SPI.begin();        // Initialize SPI bus
}

void loop() {
  digitalWrite(SS, LOW);          // Select the SPI device
  byte response = SPI.transfer(0x42); // Send byte 0x42 and receive response
  digitalWrite(SS, HIGH);         // Deselect the SPI device
  delay(1000);
}

Example

This example shows how to send a byte to an SPI device and read the response. It uses the built-in SPI library and controls the Slave Select pin manually.

arduino

#include <SPI.h>

const int slaveSelectPin = 10; // Common SS pin for SPI devices

void setup() {
  Serial.begin(9600);
  pinMode(slaveSelectPin, OUTPUT);
  SPI.begin();
}

void loop() {
  digitalWrite(slaveSelectPin, LOW);          // Select the device
  byte sentData = 0x55;                       // Data to send
  byte receivedData = SPI.transfer(sentData); // Send and receive
  digitalWrite(slaveSelectPin, HIGH);         // Deselect the device

  Serial.print("Sent: 0x");
  Serial.print(sentData, HEX);
  Serial.print(" | Received: 0x");
  Serial.println(receivedData, HEX);

  delay(1000);
}

Output

Sent: 0x55 | Received: 0x0

Common Pitfalls

Common mistakes when using SPI in Arduino include:

• Not setting the Slave Select (SS) pin as OUTPUT, which can cause the Arduino to become an SPI slave unintentionally.
• Forgetting to pull the SS pin LOW before communication and HIGH after, which can confuse the SPI device.
• Not matching SPI settings (clock speed, data order, mode) with the device requirements.
• Using SPI.transfer() without checking device datasheets for proper command sequences.

Example of wrong and right SS pin handling:

arduino

// Wrong way: Not controlling SS pin
#include <SPI.h>

void setup() {
  SPI.begin();
}

void loop() {
  SPI.transfer(0xFF); // No SS control, device may not respond
  delay(1000);
}

// Right way: Control SS pin
#include <SPI.h>

const int ssPin = 10;

void setup() {
  pinMode(ssPin, OUTPUT);
  SPI.begin();
}

void loop() {
  digitalWrite(ssPin, LOW);  // Select device
  SPI.transfer(0xFF);
  digitalWrite(ssPin, HIGH); // Deselect device
  delay(1000);
}

Quick Reference

Here is a quick cheat sheet for SPI functions and pins in Arduino:

Function/Pin	Description
#include <SPI.h>	Include SPI library
SPI.begin()	Initialize SPI bus
SPI.transfer(byte)	Send and receive a byte over SPI
pinMode(SS, OUTPUT)	Set Slave Select pin as output
digitalWrite(SS, LOW/HIGH)	Select/Deselect SPI device
SPI.setClockDivider(divider)	Set SPI clock speed
SPI.setDataMode(mode)	Set SPI mode (0-3)
SPI.setBitOrder(order)	Set bit order (MSBFIRST or LSBFIRST)

Key Takeaways

Always include SPI.h and call SPI.begin() to start SPI communication.

Manually control the Slave Select (SS) pin to select the SPI device before transfer and deselect after.

Use SPI.transfer() to send and receive data bytes over SPI.

Match SPI settings like clock speed and mode to your device's requirements.

Common errors include not setting SS pin as output and not toggling it properly.