AT90USB1286-16MU ATMEL [ATMEL Corporation], AT90USB1286-16MU Datasheet - Page 43

• Manufacturer Part Number: AT90USB1286-16MU
• Description: Microcontroller with 64/128K Bytes of ISP Flash and USB Controller
• Manufacturer: ATMEL [ATMEL Corporation]

6.4
6.5
7593A–AVR–02/06
Low Frequency Crystal Oscillator
Calibrated Internal RC Oscillator
Table 6-5.
Note:
The device can utilize a 32.768 kHz watch crystal as clock source by a dedicated Low Fre-
quency Crystal Oscillator. The crystal should be connected as shown in
Oscillator is selected, start-up times are determined by the SUT Fuses and CKSEL0 as shown in
Table
Table 6-6.
Note:
The calibrated internal RC Oscillator by default provides a 8.0 MHz clock. The frequency is nom-
inal value at 3V and 25°C. The device is shipped with the CKDIV8 Fuse programmed. See
“System Clock Prescaler” on page 47
clock by programming the CKSEL Fuses as shown in
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
Power Conditions
BOD enabled
Fast rising power
Slowly rising power
Power Conditions
BOD enabled
Fast rising power
Slowly rising power
BOD enabled
Fast rising power
Slowly rising power
6-6.
1.
1. These options should only be used if frequency stability at start-up is not important for the
The device is shipped with this option selected.
application.
Start-up times for the internal calibrated RC Oscillator clock selection
Start-up Times for the Low Frequency Crystal Oscillator Clock Selection
Start-up Time from Power-
Start-up Time from
Power-down and
down and Power-save
Reserved
Reserved
Power-save
32K CK
32K CK
32K CK
1K CK
1K CK
1K CK
Reserved
6 CK
6 CK
6 CK
for more details. This clock may be selected as the system
Additional Delay
14CK + 4.1 ms
14CK + 65 ms
14CK + 4.1 ms
14CK + 65 ms
(V
from Reset
CC
14CK
14CK
Additional Delay from
Table
= 5.0V)
Reset (V
14CK + 65 ms
(1)
14CK + 4.1 ms
6-7. If selected, it will operate with
(1)
(1)
14CK
CC
AT90USB64/128
= 5.0V)
CKSEL0
(1)
0
0
0
0
1
1
1
1
Figure
SUT1..0
SUT1..0
6-2. When this
00
01
10
11
00
01
10
00
01
10
11
11
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