ATmega88PA Automotive Atmel Corporation, ATmega88PA Automotive Datasheet - Page 29

• Manufacturer Part Number: ATmega88PA Automotive
• Manufacturer: Atmel Corporation

7.6
7.7
7701E–AVR–02/11
Calibrated Internal RC Oscillator
External Clock
By default, the Internal RC Oscillator provides an approximate 8MHz clock. Though voltage
and temperature dependent, this clock can be very accurately calibrated by the user. See
Table 22-2 on page 180
device is shipped with the CKDIV8 Fuse programmed. See
31
This clock may be selected as the system clock by programming the CKSEL Fuses as shown
in
loads the pre-programmed calibration value into the OSCCAL Register and thereby automati-
cally calibrates the RC Oscillator. The accuracy of this calibration is shown as Factory
calibration in
By changing the OSCCAL register from SW, see
on page
tion. 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 7-6.
Note:
When this Oscillator is selected, start-up times are determined by the SUT Fuses as shown in
Table 7-7 on page
Table 7-7.
Note:
To drive the device from an external clock source, CLKI should be driven as shown in
7-3 on page
grammed to “0000”.
SUT1..0
Table
for more details.
10
00
01
11
(1)
1. The device is shipped with this option selected.
1. The device is shipped with this option selected.
7-6. If selected, it will operate with no external components. During reset, hardware
32, it is possible to get higher calibration accuracy than by using the factory calibra-
Table 22-2 on page
CKSEL3..0
30. To run the device on an external clock, the CKSEL Fuses must be pro-
Internal Calibrated RC Oscillator Operating Modes
Start-up Times for the Internal Calibrated RC Oscillator Clock Selection
0010
from Power-down
29..
(1)
Start-up Time
6 CK
6 CK
6 CK
and
Atmel ATtiny24/44/84 [Preliminary]
“Internal Oscillator Speed” on page 204
“Calibration Byte” on page
180.
Additional Delay from
Reset (V
Reserved
14CK + 64 ms
14CK + 4 ms
“Oscillator Calibration Register – OSCCAL”
14CK
CC
Nominal Frequency
= 5.0V)
“System Clock Prescaler” on page
165.
8.0 MHz
Table 22-2 on page
Recommended Usage
BOD enabled
Fast rising power
Slowly rising power
for more details. The
Figure
180.
29