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Timer/Counter
Timer/Counter Prescaler
8-bit Timer/Counter0
AT90S/LS2323/2343
28
The AT90S2323/2343 provides one general-purpose 8-bit Timer/Counter –
Timer/Counter0. The Timer/Counter has prescaling selection from the 10-bit prescaling
timer. The Timer/Counter can be used either as a timer with an internal clock time base
or as a counter with an external pin connection that triggers the counting.
Figure 29 shows the Timer/Counter prescaler.
Figure 29. Timer/Counter0 Prescaler
CK
T0
CS00
CS01
CS02
The four different prescaled selections are: CK/8, CK/64, CK/256 and CK/1024, where
CK is the oscillator clock. CK, external source and stop can also be selected as clock
sources.
Figure 30 shows the block diagram for Timer/Counter0.
The 8-bit Timer/Counter0 can select clock source from CK, prescaled CK or an external
pin. In addition, it can be stopped as described in the specification for the
Timer/Counter0 Control Register (TCCR0). The overflow status flag is found in the
Timer/Counter Interrupt Flag Register (TIFR). Control signals are found in the
Timer/Counter0 Control Register (TCCR0). The interrupt enable/disable settings for
Timer/Counter0 are found in the Timer/Counter Interrupt Mask Register (TIMSK).
When Timer/Counter0 is externally clocked, the external signal is synchronized with the
oscillator frequency of the CPU. To ensure proper sampling of the external clock, the
minimum time between two external clock transitions must be at least one internal CPU
clock period. The external clock signal is sampled on the rising edge of the internal CPU
clock.
The 8-bit Timer/Counter0 features both a high-resolution and a high-accuracy usage
with the lower prescaling opportunities. Similarly, the high prescaling opportunities make
the Timer/Counter0 useful for lower speed functions or exact timing functions with infre-
quent actions.
10-BIT T/C PRESCALER
0
TIMER/COUNTER0 CLOCK SOURCE
TCK0
1004D–09/01
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