Table 6-4.
Start-up Times for the Low Power Crystal Oscillator Clock Selection (Continued)
Start-up Time from
Power-down and
Power-save
Additional Delay
from Reset
Oscillator Source /
Power Conditions
CLKSEL
0
(VCC = 5.0V)
SUT1..0
Crystal Oscillator, BOD
enabled
16K CK
16K CK
16K CK
14CK
1
1
1
01
Crystal Oscillator, fast
rising power
14CK + 4.1 ms
14CK + 65 ms
10
11
Crystal Oscillator, slowly
rising power
Notes: 1. These options should only be used when not operating close to the maximum frequency 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 frequency stability
at start-up. They can also be used with crystals when not operating close to the maximum fre-
quency of the device, and if frequency stability at start-up is not important for the application.
Table 6-5.
Start-up times for the internal calibrated RC Oscillator clock selection
Start-up Time from Power-
down and Power-save
Additional Delay from
Reset (VCC = 5.0V)
Power Conditions
BOD enabled
SUT1..0
00
6 CK
6 CK
14CK
Fast rising power
Slowly rising power
14CK + 4.1 ms
14CK + 65 ms(1)
01
6 CK
10
Reserved
11
Note:
1. The device is shipped with this option selected.
6.5
Calibrated Internal RC Oscillator
The calibrated internal RC Oscillator by default provides a 8.0 MHz clock. The fre-
quency is nominal value at 3.0V and 25°C. At 3.0V and 25°C, this calibration gives a
frequency of 8 MHz ± 10%. The device is shipped with the CKDIV8 Fuse programmed.
See “System Clock Prescaler” on page 34 for more details. This clock may be selected
as the system clock by programming the CKSEL Fuses as shown in Table 6-6. 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 3.3V 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 246
Table 6-6.
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.
32
AT90USB82/162
7707D–AVR–07/08
ATMEL [ ATMEL ]
