ultrasonic phased array

Question

I have the following code for Arduino mega to output 40 kHz square waves at the analog pins. I need to apply specific phase delays for the signals at each pin though and am struggling to find out how to do this. Any help would be appreciated. Thanks!

byte TP = 0b10101010; // Every other port receives the inverted signal

void setup() {

DDRF = 0b11111111; // Set all analog ports to be outputs
DDRK = 0b11111111; // Set all analog ports to be outputs
// Initialize Timer1

noInterrupts(); // Disable interrupts

TCCR1A = 0;

TCCR1B = 0;

TCNT1 = 0;

OCR1A = 200; // Set compare register (16MHz / 200 = 80kHz square wave -> 40kHz full wave)

TCCR1B |= (1 << WGM12); // CTC mode

TCCR1B |= (1 << CS10); // Set prescaler to 1 ==> no prescaling

TIMSK1 |= (1 << OCIE1A); // Enable compare timer interrupt

interrupts(); // Enable interrupts

}

ISR(TIMER1_COMPA_vect) {

PORTF = TP; // Send the value of TP to the outputs
PORTK = TP;
TP = ~TP; // Invert TP for the next run

}

void loop() {

// Nothing left to do here :)

}