#include <SPI.h>
#define MAX7219_REG_DECODEMODE 0x09
#define MAX7219_REG_INTENSITY 0x0A
#define MAX7219_REG_SCANLIMIT 0x0B
#define MAX7219_REG_SHUTDOWN 0x0C
#define MAX7219_REG_DISPLAYTEST 0x0F

const int csPin = 10;

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

  sendCommand(MAX7219_REG_DECODEMODE, 0x00);
  sendCommand(MAX7219_REG_INTENSITY, 0x0A);
  sendCommand(MAX7219_REG_SCANLIMIT, 0x07);
  sendCommand(MAX7219_REG_SHUTDOWN, 0x01);
  sendCommand(MAX7219_REG_DISPLAYTEST, 0x00);

  sendCommand(1, 0b00000000);
  sendCommand(2, 0b01000010);
  sendCommand(3, 0b10100101);
  sendCommand(4, 0b00000000);
  sendCommand(5, 0b00011000);
  sendCommand(6, 0b01000010);
  sendCommand(7, 0b00111100);
  sendCommand(8, 0b00011000);
}

void loop() {

}

void sendCommand(byte reg, byte data) {
  digitalWrite(csPin, LOW);
  SPI.transfer(reg);
  SPI.transfer(data);
  digitalWrite(csPin, HIGH);
}