at90pwm81-16se ATMEL Corporation, at90pwm81-16se Datasheet - Page 30

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

30
AT90PWM81
The switch between 8 MHz and 1 MHz is done by the CKRC81 bit in MCUCR register. See
trol Register – MCUCR” on page 41
CSEL configurations. At reset, the CKRC81 bit is initialised with the value compatible with CKSEL value
(1 for CKSEL3..0 = 0110, 0 for all other values).
The RC oscillator is active for any CKSEL3..0 or CSEL3..0 configuration where it is used as system clock
or PLL source clock. The RC oscillator is diabled in the following CKSEL3..0 or CSEL3..0 cases:
•
•
•
The device is shipped with the CKDIV8 Fuse programmed. See
more details. This clock may be selected as the system clock by programming the CKSEL Fuses or CSEL
field as shown in
ware loads the calibration byte into the OSCCAL Register and thereby automatically calibrates the RC
Oscillator.The accuracy of this calibration is shown as Factory calibration in
By changing the OSCCAL register from SW, see
38, it is possible to get a higher calibration accuracy than by using the factory calibration. The accuracy of
this calibration is shown as User calibration in
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
Table 6-3.
Notes:
When this Oscillator is selected, start-up times are determined by the SUT Fuses as shown in
page
Table 6-4.
Note:
Power Conditions
BOD enabled
Fast rising power
Slowly rising power
0011 (128k oscillator)
0100, 0101 (PLL/4 system clock driven by external clock or oscillator)
1100,1101 (External oscillator)
30.
“Calibration Byte” on page
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 V
4. Switch between 8 MHz and 1 MHz is done by CKRC81 bit in MCUCR register.
1. If the RSTDISBL fuse is programmed, this start-up time will be increased to
2.
programmed in order to divide the internal frequency by 8.
14CK + 4.1 ms to ensure programming mode can be entered.
The device is shipped with this option selected.
Internal Calibrated RC Oscillator Operating Modes
Start-up times for the internal calibrated RC Oscillator clock selection
Table
Frequency Range
6-1. If selected, it will operate with no external components. During reset, hard-
0.95 - 1.05
7.6 - 8.4
Start-up Time from Power-down
252.
(2)
(4)
for more details.The RC oscillator can be accessed by two CKSEL or
(MHz)
Reserved
6 CK
6 CK
6 CK
Table 25-1 on page 277
“OSCCAL – Oscillator Calibration Register” on page
“System Clock Prescaler” on page 38
(1)(3)
Additional Delay from
Reset (V
14CK + 65 ms
14CK + 4.1 ms
14CK
Table 25-1 on page
CC
CC
CKSEL3..0
(1)
), the CKDIV8 Fuse can be
= 5.0V)
0010
0010
(2)
7734M–AVR–03/10
Table 6-4 on
“MCU Con-
SUT1..0
277.
00
01
10
11
for