~2.7 MHz
void setup()
{
pinMode(4, OUTPUT);
}
void loop()
{
noInterrupts();
while (true)
{
//~2.7MHz
PIND = 0x10; // Toggles pin D04
//Toggle pins specific to UNO
//PINB=0x20; //13 PINB=0x10; //12 PINB=0x08; //11 PINB=0x04; //10 PINB=0x02; //9 PINB=0x01; //8
//PIND=0x80; //7 PIND=0x40; //6 PIND=0x20; //5 PIND=0x10; //4 PIND=0x08; //3 PIND=0x04; //2
}
interrupts();
}