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AT90S8414
Preliminary
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, added selections as CK, external source and stop, can be selected as clock sources.
The 8-Bit Timer/Counter0
Figure 32 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 different status flags
(overflow and compare match) and 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 assure proper sampling of the external clock, the minimum time for the external clock being low and high 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 infrequent actions.
Figure 32: Timer/Counter0 Block Diagram
The Timer/Counter0 supports an Output Compare function using the Output Compare Register 0 - OCR0 as the data
source to be compared to the Timer/Counter0 contents. The Output Compare functions include optional clearing of the
counter on compare matches, and actions on the Output Compare pin 0 on compare matches. The Output Compare pin 0
function makes the Timer/Counter0 useful for PWM (Pulse Width Modulation) functions.
Содержание AT90S8414
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