ATMEGA163 ATMEL [ATMEL Corporation], ATMEGA163 Datasheet - Page 40

• Manufacturer Part Number: ATMEGA163
• Description: 8-bit Microcontroller with 16K Bytes In-System Programmable Flash
• Manufacturer: ATMEL [ATMEL Corporation]

8-bit Timer/Counter0
40
ATmega163(L)
Figure 31. Prescaler for Timer/Counter2
The clock source for Timer/Counter2 is named PCK2. PCK2 is by default connected to
the main system clock CK. By setting the AS2 bit in ASSR, Timer/Counter2 is asynchro-
nously clocked from the PC6(TOSC1) pin. This enables use of Timer/Counter2 as a
Real Time Clock (RTC). When AS2 is set, pins PC6(TOSC1) and PC7(TOSC2) are dis-
connected from Port C. A crystal can then be connected between the PC6(TOSC1) and
PC7(TOSC2) pins to serve as an independent clock source for Timer/Counter2. The
Oscillator is optimized for use with a 32.768 kHz crystal. Applying an external clock
source to TOSC1 is not recommended. Setting the PSR2 bit in SFIOR resets the pres-
caler. This allows the user to operate with a predictable prescaler.
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 “Timer/Counter0 Control Register –
TCCR0” on page 41. The overflow Status Flag is found in “The Timer/Counter Interrupt
Flag Register – TIFR” on page 32. Control signals are found in the Timer/Counter0 Con-
trol Register – TCCR0. The interrupt enable/disable settings for Timer/Counter0 are
found in “The Timer/Counter Interrupt Mask Register – TIMSK” on page 31.
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 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.
TOSC1
PSR2
CS20
CS21
CS22
AS2
CK
PCK2
Clear
TIMER/COUNTER2 CLOCK SOURCE
0
10-BIT T/C PRESCALER
TCK2
1142E–AVR–02/03