ATMEGA48V_11 ATMEL [ATMEL Corporation], ATMEGA48V_11 Datasheet - Page 33

• Manufacturer Part Number: ATMEGA48V_11
• Description: 8-bit Atmel Microcontroller with 4/8/16K Bytes In-System Programmable Flash
• Manufacturer: ATMEL [ATMEL Corporation]

9.5
9.6
2545T–AVR–05/11
Low frequency crystal oscillator
Calibrated internal RC oscillator
The device can utilize a 32.768kHz watch crystal as clock source by a dedicated low frequency
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 9-7.
Note:
By default, the internal RC oscillator provides an approximate 8.0MHz clock. Though voltage
and temperature dependent, this clock can be very accurately calibrated by the user. 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 as shown in
Table 9-8 on page
hardware loads the pre-programmed calibration value 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
page
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 calibra-
tion value, see the section
Power conditions
BOD enabled
Fast rising power
Slowly rising power
BOD enabled
Fast rising power
Slowly rising power
37, it is possible to get a higher calibration accuracy than by using the factory calibration.
9-7.
1. These options should only be used if frequency stability at start-up is not important for the
application.
Table 29-1 on page
Start-up times for the low frequency crystal oscillator clock selection.
34. If selected, it will operate with no external components. During reset,
“Calibration byte” on page
Start-up time from
power-down and
Reserved
Reserved
power-save
306.
32KCK
32KCK
32KCK
1KCK
1KCK
1KCK
“OSCCAL – Oscillator calibration register” on
288.
Additional delay
“System clock prescaler” on page 36
14CK + 4.1ms
14CK + 65ms
14CK + 4.1ms
14CK + 65ms
(V
from reset
CC
14CK
14CK
= 5.0V)
ATmega48/88/168
Figure 9-2 on page
Table 29-1 on page
(1)
(1)
(1)
CKSEL0
1
1
0
0
0
0
1
1
30. When this
306.
SUT1..0
00
01
10
11
00
01
10
11
for
33