ATMEGA169 ATMEL [ATMEL Corporation], ATMEGA169 Datasheet - Page 27

• Manufacturer Part Number: ATMEGA169
• Description: 8-bit Microcontroller with 16K Bytes In-System Programmable Flash
• Manufacturer: ATMEL [ATMEL Corporation]

Calibrated Internal RC
Oscillator
2514P–AVR–07/06
Table 7. Start-up Times for the Low-frequency Crystal Oscillator Clock Selection
Note:
The calibrated internal RC Oscillator provides a fixed 8.0 MHz clock. The frequency is
nominal value at 3V and 25°C. If 8 MHz frequency exceeds the specification of the
device (depends on V
internal frequency by 8 during start-up. The device is shipped with the CKDIV8 Fuse
programmed. See “System Clock Prescaler” on page 29. for more details. This clock
may be selected as the system clock by programming the CKSEL Fuses as shown in
Table 8. If selected, it will operate with no external components. During reset, hardware
loads the calibration byte into the OSCCAL Register and thereby automatically cali-
brates the RC Oscillator. At 3V and 25°C, this calibration gives a frequency within ± 10%
of the nominal frequency. Using calibration methods as described in application notes
available at www.atmel.com/avr it is possible to achieve ± 2% accuracy at any given V
and Temperature. When this Oscillator is used as the chip clock, the Watchdog Oscilla-
tor 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 269.
Table 8. Internal Calibrated RC Oscillator Operating Modes
Note:
When this Oscillator is selected, start-up times are determined by the SUT Fuses as
shown in Table 9. Selecting internal RC Oscillator allows the XTAL1/TOSC1 and
XTAL2/TOSC2 pins to be used as timer oscillator pins.
Table 9. Start-up times for the internal calibrated RC Oscillator clock selection
Note:
CKSEL3..0
SUT1..0
10
0110
00
01
11
0111
(1)
(1)
1. This option should only be used if frequency stability at start-up is not important for
1. The device is shipped with this option selected.
1. The device is shipped with this option selected.
the application
CKSEL3..0
Start-up Time from Power-
down and Power-save
0010
CC
Power-down and Power-save
6 CK
6 CK
6 CK
), the CKDIV8 Fuse must be programmed in order to divide the
Start-up Time from
32K CK
1K CK
Additional Delay from
Reset (V
Reserved
14CK + 4.1 ms
14CK + 65 ms
14CK
CC
Nominal Frequency
= 5.0V)
8.0 MHz
(1)
ATmega169/V
Recommended Usage
Stable frequency at start-up
Recommended Usage
BOD enabled
Fast rising power
Slowly rising power
27
CC