The AT90S8535 provides three general-purpose Timer/Counters – two 8-bit T/Cs and
one 16-bit T/C. Timer/Counter2 can optionally be asynchronously clocked from an exter-
nal oscillator. This oscillator is optimized for use with a 32.768 kHz watch crystal,
enabling use of Timer/Counter2 as a Real-time Clock (RTC). Timer/Counters 0 and 1
have individual prescaling selection from the same 10-bit prescaling timer.
Timer/Counter2 has its own prescaler. These Timer/Counters can either be used as a
timer with an internal clock time base or as a counter with an external pin connection
that triggers the counting.
Figure 28. Prescaler for Timer/Counter0 and 1
For Timer/Counters 0 and 1, the four different prescaled selections are: CK/8, CK/64,
CK/256 and CK/1024, where CK is the oscillator clock. For the two Timer/Counters 0
and 1, CK, external source and stop can also be selected as clock sources.
Figure 29. Timer/Counter2 Prescaler
10-BIT T/C PRESCALER
TIMER/COUNTER2 CLOCK SOURCE