AT90PWM2(2005) View Datasheet(PDF) - Atmel Corporation
Part Name
Description
Manufacturer
AT90PWM2
(Rev.:2005)
(Rev.:2005)
Atmel Corporation
AT90PWM2 Datasheet PDF : 365 Pages
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AT90PWM2/3
Calibrated Internal RC
Oscillator
Table 6. Start-up Times for the Oscillator Clock Selection
CKSEL0 SUT1..0
0
00
Start-up Time from
Power-down and
Power-save
258 CK(1)
0
01
258 CK(1)
0
10
1K CK(2)
Additional Delay
from Reset
(VCC = 5.0V)
14CK + 4.1 ms
14CK + 65 ms
14CK
Recommended Usage
Ceramic resonator, fast
rising power
Ceramic resonator,
slowly rising power
Ceramic resonator,
BOD enabled
0
11
1
00
1K CK(2)
1K CK(2)
14CK + 4.1 ms
14CK + 65 ms
Ceramic resonator, fast
rising power
Ceramic resonator,
slowly rising power
1
01
16K CK
14CK
Crystal Oscillator, BOD
enabled
1
10
16K CK
14CK + 4.1 ms
Crystal Oscillator, fast
rising power
1
11
16K CK
14CK + 65 ms
Crystal Oscillator,
slowly rising power
Notes:
1. These options should only be used when not operating close to the maximum fre-
quency of the device, and only if frequency stability at start-up is not important for the
application. These options are not suitable for crystals.
2. These options are intended for use with ceramic resonators and will ensure fre-
quency stability at start-up. They can also be used with crystals when not operating
close to the maximum frequency of the device, and if frequency stability at start-up is
not important for the application.
The calibrated internal RC Oscillator by default provides a 8.0 MHz clock. The frequency
is nominal value at 3V and 25°C. The device is shipped with the CKDIV8 Fuse pro-
grammed. See “System Clock Prescaler” on page 37 for more details. This clock may
be selected as the system clock by programming the CKSEL Fuses as shown in Table
3. If selected, it will operate with no external components. During reset, hardware loads
the calibration byte into the OSCCAL Register and thereby automatically calibrates the
RC Oscillator. At 3V and 25°C, this calibration gives a frequency of 8 MHz ± 1%. The
oscillator can be calibrated to any frequency in the range 7.3 - 8.1 MHz within ±1%
accuracy, by changing the OSCCAL register. When this Oscillator is used as the chip
clock, the Watchdog Oscillator will still be used for the Watchdog Timer and for the
Reset Time-out. For more information on the pre-programmed calibration value, see the
section “Calibration Byte” on page 291.
Table 7. Internal Calibrated RC Oscillator Operating Modes(1)(3)
Frequency Range(2) (MHz)
CKSEL3..0
7.3 - 8.1
0010
Notes:
1. The device is shipped with this option selected.
2. The frequency ranges are preliminary values. Actual values are TBD.
3. If 8 MHz frequency exceeds the specification of the device (depends on VCC), the
CKDIV8 Fuse can be programmed in order to divide the internal frequency by 8.
33
4317B–AVR–02/05
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