Data Sheet

34
2545K–AVR–04/07
ATmega48/88/168
3. If 8 MHz frequency exceeds the specification of the device (depends on V
CC
), the CKDIV8
Fuse can be programmed in order to divide the internal frequency by 8.
When this Oscillator is selected, start-up times are determined by the SUT Fuses as shown in
Table 7-9 on page 34.
Note: 1. If the RSTDISBL fuse is programmed, this start-up time will be increased to
14CK + 4.1 ms to ensure programming mode can be entered.
2. The device is shipped with this option selected.
7.7 128 kHz Internal Oscillator
The 128 kHz internal Oscillator is a low power Oscillator providing a clock of 128 kHz. The fre-
quency is nominal at 3V and 25°C. This clock may be select as the system clock by
programming the CKSEL Fuses to “11” as shown in Table 7-10.
Note: 1. The frequency is preliminary value. Actual value is TBD.
When this clock source is selected, start-up times are determined by the SUT Fuses as shown in
Table 7-11.
Note: 1. If the RSTDISBL fuse is programmed, this start-up time will be increased to
14CK + 4.1 ms to ensure programming mode can be entered.
Table 7-9. Start-up times for the internal calibrated RC Oscillator clock selection
Power Conditions
Start-up Time from Power-
down and Power-save
Additional Delay from
Reset (V
CC
= 5.0V) SUT1..0
BOD enabled 6 CK 14CK
(1)
00
Fast rising power 6 CK 14CK + 4.1 ms 01
Slowly rising power 6 CK 14CK + 65 ms
(2)
10
Reserved 11
Table 7-10. 128 kHz Internal Oscillator Operating Modes
Nominal Frequency CKSEL3..0
128 kHz 0011
Table 7-11. Start-up Times for the 128 kHz Internal Oscillator
Power Conditions
Start-up Time from Power-
down and Power-save
Additional Delay from
Reset SUT1..0
BOD enabled 6 CK 14CK
(1)
00
Fast rising power 6 CK 14CK + 4 ms 01
Slowly rising power 6 CK 14CK + 64 ms 10
Reserved 11