AT90PWM81 View Datasheet(PDF) - Atmel Corporation
Part Name
Description
MFG CO.
'AT90PWM81' PDF : 325 Pages View PDF
AT90PWM81/161
5.2.2.1
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.
5.2.3
128KHz Internal Oscillator
The 128kHz internal Oscillator is a low power Oscillator providing a clock of 128kHz. The fre-
quency 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 Table 5-1 on page 28.
When this clock source is selected, start-up times are determined by the SUT Fuses or by CSUT
field as shown in Table 5-5.
Table 5-5. Start-up times for the 128kHz internal oscillator.
SUT1..0 (1)
CSUT1..0 (2)
Start-up time from power-
down
Additional delay from
reset
00
6 CK
14CK
01
6 CK
14CK + 4ms
10
6 CK
14CK + 64ms
11
Reserved
Recommended
usage
BOD enabled
Fast rising power
Slowly rising power
Notes: 1. Flash Fuse bits.
2. CLKSELR register bits.
5.2.4
Crystal Oscillator
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 Figure 5-2 on page 31. Either a quartz
crystal or a ceramic resonator 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 5-6. For ceramic resonators, the capacitor values given by
the manufacturer should be used.
Figure 5-2. Crystal oscillator connections.
C2
XTAL2
C1
XTAL1
GND
31
7734Q–AVR–02/12
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