Datasheet

Power Conditions Start-Up Time from Power-Down
and Power-Save
Additional Delay from Reset (V
CC
= 5.0V) SUT[1:0]
Slow rising power 6 CK 19CK + 65 ms
(2)
10
Reserved 11
Note:
1. If the RSTDISBL fuse is programmed, this start-up time will be increased to
19CK + 4 ms to ensure programming mode can be entered.
2. The device is shipped with this option selected.
Related Links
System Clock Prescaler
Clock Characteristics
Calibration Byte
Internal Oscillator Speed
OSCCAL
11.6 128 kHz Internal Oscillator
The 128 kHz internal oscillator is a low-power oscillator providing a clock of 128 kHz. This clock may be
select as the system clock by programming the CKSEL fuses to '0011' as shown in the following table.
Warning: Using the 128 kHz internal oscillator as the system oscillator and Watchdog Timer
simultaneously is not recommended as this defeats one of the purposes of the Watchdog Timer.
Table 11-12. 128 kHz Internal Oscillator Operating Modes
Nominal Frequency
(1)
CKSEL[3:0]
128 kHz 0011
Note:
1. The 128 kHz oscillator is a very low-power clock source, and is not designed for high accuracy.
When this clock source is selected, start-up times are determined by the SUT fuses:
Table 11-13. Start-Up Times for the 128 kHz Internal Oscillator
Power Conditions Start-Up Time from Power-Down
and Power-Save
Additional Delay from Reset SUT[1:0]
BOD enabled 6CK 19CK
(1)
00
Fast rising power 6CK 19CK + 4 ms 01
Slowly rising power 6CK 19CK + 65 ms 10
Reserved 11
Note:
1. If the RSTDISBL fuse is programmed, this start-up time will be increased to
19CK + 4 ms to ensure programming mode can be entered.
ATmega328PB
System Clock and Clock Options
© 2018 Microchip Technology Inc.
Datasheet Complete
DS40001906C-page 53