atmega32c1 ATMEL Corporation, atmega32c1 Datasheet - Page 31

• Manufacturer Part Number: atmega32c1
• Description: Atmega32m1 Automotive 8-bit Avr Microcontroller With 32k/64k Bytes In-system Programmable Flash
• Manufacturer: ATMEL Corporation

5.3
5.4
7647A–AVR–02/08
Default Clock Source
Low Power Crystal Oscillator
frequency of the Watchdog Oscillator is voltage dependent as shown in
Frequency vs. VCC” on page
Table 5-2.
The device is shipped with CKSEL = “0010”, SUT = “10”, and CKDIV8 programmed. The default
clock source setting is the Internal RC Oscillator with longest start-up time and an initial system
clock prescaling of 8. This default setting ensures that all users can make their desired clock
source setting using an In-System or Parallel programmer.
XTAL1 and XTAL2 are input and output, respectively, of an inverting amplifier which can be con-
figured for use as an On-chip Oscillator, as shown in
ceramic resonator may be used.
This Crystal Oscillator is a low power oscillator, with reduced voltage swing on the XTAL2 out-
put. It gives the lowest power consumption, but is not capable of driving other clock inputs.
C1 and C2 should always be equal for both crystals and resonators. The optimal value of the
capacitors depends on the crystal or resonator in use, the amount of stray capacitance, and the
electromagnetic noise of the environment. Some initial guidelines for choosing capacitors for
use with crystals are given in
the manufacturer should be used. For more information on how to choose capacitors and other
details on Oscillator operation, refer to the Multi-purpose Oscillator Application Note.
Figure 5-2.
The Oscillator can operate in three different modes, each optimized for a specific frequency
range. The operating mode is selected by the fuses CKSEL3..1 as shown in
Table 5-3.
CKSEL3..1
Typ Time-out (V
100
(2)
4.1 ms
65 ms
Number of Watchdog Oscillator Cycles
Crystal Oscillator Connections
Crystal Oscillator Operating Modes
Frequency Range
CC
= 5.0V)
0.4 - 0.9
339.
Table
5-3. For ceramic resonators, the capacitor values given by
(1)
Typ Time-out (V
(MHz)
C2
C1
4.3 ms
69 ms
Recommended Range for Capacitors C1 and
CC
= 3.0V)
Figure
ATmega32/64/M1/C1
C2 for Use with Crystals (pF)
XTAL2
XTAL1
GND
5-2. Either a quartz crystal or a
–
Number of Cycles
“Watchdog Oscillator
64K (65,536)
4K (4,096)
Table
5-3.
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