at90pwm81-16se ATMEL Corporation, at90pwm81-16se Datasheet - Page 31

• Manufacturer Part Number: at90pwm81-16se
• Description: 8-bit Avr Microcontroller With 8k Bytes In- System Programmable Flash
• Manufacturer: ATMEL Corporation

6.2.2.1
6.2.3
6.2.4
7734M–AVR–03/10
128 KHz Internal Oscillator
Crystal Oscillator
RC Oscillator calibration at Factory
The RC oscillator is calibrated at 3V, 25°C for an 8MHz target frequency with an Accuracy +/- 1%.
The corresponding value OSCAL (@Amb.) is stored in the signature row and automatically loaded in the
OSCAL register at reset.
The RC oscillator is monitored at 105°C or 125°C (versus Product version) with an accuracy within
+/- 5% limits.
The 128 KHz internal Oscillator is a low power Oscillator providing a clock of 128 KHz. The frequency is
nominal at 3V and 25⋅C. This clock may be select as the system clock by programming CKSEL Fuses or
CSEL field as shown in
When this clock source is selected, start-up times are determined by the SUT Fuses or by CSUT field as
shown in
Table 6-5.
Notes:
XTAL1 and XTAL2 are input and output, respectively, of an inverting amplifier which can be configured
for use as an On-chip Oscillator, as shown in
may be used.
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
Table
Figure 6-2.
CSUT1..0
SUT1..0
6-6. For ceramic resonators, the capacitor values given by the manufacturer should be used.
00
01
10
11
1. Flash Fuse bits
2. CLKSELR register bits
Table
(1)
(4)
6-5.
Start-up Times for the 128 kHz Internal Oscillator
Crystal Oscillator Connections
Start-up Time from Power-down
Table 6-1 on page
6 CK
6 CK
6 CK
28.
C2
C1
Figure
6-2. Either a quartz crystal or a ceramic resonator
Additional Delay
Reserved
14CK + 64 ms
14CK + 4 ms
from Reset
XTAL2
XTAL1
GND
14CK
Recommended Usage
BOD enabled
Fast rising power
Slowly rising power
AT90PWM81
31