Ard Spi Transfer

In this tutorial, you'll learn about Arduino SPI.transfer Returns 0xFF Always. We cover key concepts, practical examples, and best practices to help you understand and apply this topic effectively.

The Problem

SPI.transfer() always returns 0xFF regardless of the sent byte.

Quick Fix

Wrong

byte data = SPI.transfer(0x00);  // Returns 0xFF if MISO not connected

data = 0xFF (MISO floating high).

Right

#include <SPI.h>

const int csPin = 10;

void setup() {
  Serial.begin(9600);
  pinMode(csPin, OUTPUT);
  digitalWrite(csPin, HIGH);
  SPI.begin();
}

// Read a register from SPI device
byte readRegister(byte reg) {
  digitalWrite(csPin, LOW);
  SPI.transfer(reg);        // Send register address
  byte result = SPI.transfer(0x00);  // Read response
  digitalWrite(csPin, HIGH);
  return result;
}

void loop() {
  byte val = readRegister(0x00);
  Serial.print("Register 0x00: 0x");
  Serial.println(val, HEX);
  delay(1000);
}

Register 0x00: 0x1A  (actual value from device, not 0xFF).

Prevention

SPI.transfer() returns 0xFF if MISO is not connected or the device is not selected. Check wiring: MISO, MOSI, SCK, CS. Ensure CS is pulled LOW. Verify the device is powered. Some devices require a specific read command byte first — check the datasheet.

DodaTech engineers apply these same patterns across Doda Browser, DodaZIP, and Durga Antivirus Pro for production IoT reliability.

FAQ