AT90PWM2B-16SE ATMEL [ATMEL Corporation], AT90PWM2B-16SE Datasheet - Page 31

• Manufacturer Part Number: AT90PWM2B-16SE
• Description: 8-bit Microcontroller with 8K Bytes In-System Programmable Flash
• Manufacturer: ATMEL [ATMEL Corporation]

7.3
7.4
4317J–AVR–08/10
Default Clock Source
Low Power Crystal Oscillator
up, ensuring stable Oscillator operation before instruction execution starts. When the CPU starts
from reset, there is an additional delay allowing the power to reach a stable level before starting
normal operation. The Watchdog Oscillator is used for timing this real-time part of the start-up
time. The number of WDT Oscillator cycles used for each time-out is shown in
frequency of the Watchdog Oscillator is voltage dependent as shown in
Frequency vs. VCC” on page
Table 7-3.
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 7-3.
Typ Time-out (V
4.1 ms
65 ms
Number of Watchdog Oscillator Cycles
Crystal Oscillator Connections
CC
= 5.0V)
328.
Table
7-4. For ceramic resonators, the capacitor values given by
Typ Time-out (V
C2
C1
4.3 ms
69 ms
CC
= 3.0V)
Figure
AT90PWM2/3/2B/3B
XTAL2
XTAL1
GND
7-3. Either a quartz crystal or a
Number of Cycles
“Watchdog Oscillator
64K (65,536)
4K (4,096)
Table
7-3. The
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