atmega161-4pi ATMEL Corporation, atmega161-4pi Datasheet - Page 38

• Manufacturer Part Number: atmega161-4pi
• Description: 8-bit Microcontroller With 16k Bytes Of In-system Programmable Flash
• Manufacturer: ATMEL Corporation

Timer/Counters
Timer/Counter
Prescalers
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ATmega161(L)
The ATmega161 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. Both these prescalers can be Reset by setting
the corresponding control bits in the Special Functions IO Register (SFIOR). Refer to
page 39 for a detailed description. 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, which
triggers the counting.
Figure 29. Prescaler for Timer/Counter0 and 1
For Timer/Counters 0 and 1, the four 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. Setting the PSR10 bit
in SFIOR Resets the prescaler. This allows the user to operate with a predictable pres-
caler. Note that Timer/Counter1 and Timer/Counter0 share the same prescaler and a
Prescaler Reset will affect both Timer/Counters.
PSR10
TCK1
Clear
TCK0
1228D–AVR–02/07