Getting Started

Chapter 8: C Pointers and Arrays

peration AS2: Asynchronous Timer/Counter2, AS2

Register, ASSR.

= (1<<AS2);

lear the Timer/Counter 2, TCNT2, count register.

TCNT2 = 0;

egister,

econd and 128*256 =

nd overflows once per

UB: Timer/Counter2 Update Busy and the TCR2UB:

r/Counter Control Register2 Update Busy bits of the, ASSR, to be cleared.

| (ASSR & 0x04));

R2 = 0xFF;

mer/Counter 2 Output Interrupt Enable, TOIE2, bit in the Timer/Counter

, to enable the timer output interrupt enable.

bi(TIMSK2, TOIE2);

l interrupts.

ow the SIGNAL(SIG_OVERFLOW2) function will be called once per second

s shown in the code section) so we can use it to keep track of seconds.

Converting Computer Time to Human Readable Time

We can keep a count of seconds, but what good does it do us if our watch reads
40241? If the count started at midnight then this number of seconds would

Select Timer2 asynchronous o
bit in the Asynchronous Status

ASSR

C

Select the divide by 128 prescale factor in the Timer Counter Control R
TCCR2A. The watch crystal pulses 32768 times in one s
32768, so with a 128 prescaler, the timer counts to 256 a
second.

TCCR2A |= (1<<CS22) | (1<<CS20);

Wait for the TCN2
Time

while((ASSR & 0x01)

Clear the Timer/Counter2 Interrupt Flags Register, TIFR2.

TIF

Set the Ti
2 Interrupt Mask Register, TIMSK2

s

And finally, enable the globa

sei();

N
(a