10.6 128kHz Internal Oscillator

The 128kHz internal Oscillator is a low power Oscillator providing a clock of 128kHz. This clock may be select as the system clock by programming the CKSEL Fuses to '0011':

Table 10-11. 128kHz Internal Oscillator Operating Modes
Nominal Frequency(1) CKSEL[3:0]
128kHz0011
Note:
  1. The 128kHz 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 10-12. Start-Up Times for the 128kHz Internal Oscillator
Power ConditionsStart-Up Time from Power-down and Power-saveAdditional Delay from ResetSUT[1:0]
BOD enabled6 CK14CK00
Fast rising power6 CK14CK + 4ms01
Slowly rising power6 CK14CK + 65ms10
Reserved11