max7219_max7221_arduino.ino

#include <SPI.h>

void setup() {
      
  // We will need to control the Load/CS pin so
  // make a pin an output, for this example I'll
  // use pin 7.
  pinMode(7, OUTPUT);
  
  // The Maxim chip need the most siginifcant
  // bit first.
  SPI.setBitOrder(MSBFIRST);
  
  // Make sure that the chip is turned on
  maxTransfer(0x0C, 0x01);

  // We can use the display decode mode to
  // easily pick the character
  maxTransfer(0x09, 0xFF);
  
}

void loop() {

  // Loop through each character
  for (uint8_t i = 0; i < 0x10; ++i)
  {
      // Update the 1st digit
    maxTransfer(0x01, i);

    // Display for 500ms
    delay(500);
  }

}

void maxTransfer(uint8_t reg, uint8_t data)
{

  // Make sure that the Load/CS pin is low
  digitalWrite(7, LOW);

  // Open SPI
  SPI.begin();

  // The Maxim chip wants the register's 
  // address first
  SPI.transfer(reg);

  // Next send the data
  SPI.transfer(data);

  // End SPI
  SPI.end();

  // The Maxim chip loads the data when the
  // Load/CS pin switches from low to high
  digitalWrite(7, HIGH);

}