AT90S/LS4434 and AT90S/LS8535
30
Timer/Counters
The AT90S4434/8535 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 external 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 connec-
tion that triggers the counting.
Timer/Counter Prescalers
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
TCK1
TCK0
10-BIT T/C PRESCALER
TIMER/COUNTER2 CLOCK SOURCE
PCK2
CK
PCK2
TOSC1
AS2
CS20
CS21
CS22
PCK2/8
PCK2/64
PCK2/128
PCK2/1024
PCK2/256
PCK2/32
0
