Scrolling text on LED matrices using SPI and arduino Mega2560

Other Hardware LEDs and Multiplexing
63

Move the clear digits to immediately after the SPI.begin();

This chunk of code at the end of setup will leave display test on = all LEDs on:

byte display_test = 0x0F; // 0x00 = normal, 0x01 = display test mode all on full

  // dispay test to normal
  digitalWrite (ss0, LOW);
  SPI.transfer (display_test);
  SPI.transfer (0x01);
  digitalWrite (ss0, HIGH);

I would put in a brief delay, and then set this register to 0 to turn it off.