ATMEGA3250V_14 Datasheet, PDF (29/362 Pages) ATMEL Corporation – High Endurance Non-volatile Memory Segments

ATmega325/3250/645/6450
Table 9-4. Start-up Times for the Crystal Oscillator Clock Selection (Continued)
CKSEL0 SUT1:0
0
11
Start-up Time from
Power-down and
Power-save
1K CK⁽²⁾
1
00
1K CK⁽²⁾
Additional Delay
from Reset
(V_CC = 5.0V)
14CK + 4.1ms
14CK + 65ms
Recommended
Usage
Ceramic resonator,
fast rising power
Ceramic resonator,
slowly rising power
1
01
16K CK
14CK
Crystal Oscillator,
BOD enabled
1
10
16K CK
14CK + 4.1ms
Crystal Oscillator, fast
rising power
1
Note:
11
16K CK
14CK + 65ms
Crystal Oscillator,
slowly rising power
1. These options should only be used when not operating close to the maximum frequency of the
device, and only if frequency stability at start-up is not important for the application. These
options are not suitable for crystals.
2. These options are intended for use with ceramic resonators and will ensure frequency stability
at start-up. They can also be used with crystals when not operating close to the maximum fre-
quency of the device, and if frequency stability at start-up is not important for the application.
9.4 Low-frequency Crystal Oscillator
To use a 32.768 kHz watch crystal as the clock source for the device, the low-frequency crystal
Oscillator must be selected by setting the CKSEL Fuses to “0110” or “0111”. The crystal should
be connected as shown in Figure 9-2 on page 28. When this Oscillator is selected, start-up times
are determined by the SUT Fuses as shown in Table 9-5 on page 29 and CKSEL1..0 as shown
in Table 9-6 on page 29.
Table 9-5. Start-up Times for the Low-frequency Crystal Oscillator Clock Selection
SUT1..0
00
Additional Delay from Reset (V_CC = 5.0V) Recommended Usage
14CK
Fast rising power or BOD enabled
01
14CK + 4.1ms
Slowly rising power
10
14CK + 65ms
Stable frequency at start-up
11
Reserved
Table 9-6. Start-up Times for the Low-frequency Crystal Oscillator Clock Selection
CKSEL3..0
0110^(Note:)
Start-up Time from
Power-down and Power-save
1K CK
Recommended Usage
0111
32K CK
Stable frequency at start-up
Note: This option should only be used if frequency stability at start-up is not important for the application
9.5 Calibrated Internal RC Oscillator
The calibrated Internal RC Oscillator by default provides a 8.0MHz 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 32 for more details.
29
2570N–AVR–05/11