Datasheet
28
ATtiny25/45/85 [DATASHEET]
2586Q–AVR–08/2013
When the calibrated 8 MHz internal oscillator is selected as clock source the start-up times are determined by the
SUT Fuses as shown in Table 6-7 below.
Note: 1. If the RSTDISBL fuse is programmed, this start-up time will be increased to 14CK + 4 ms to ensure programming
mode can be entered.
2. The device is shipped with this option selected.
In ATtiny15 Compatibility Mode start-up times are determined by SUT fuses as shown in Table 6-8 below.
Note: 1. If the RSTDISBL fuse is programmed, this start-up time will be increased to 14CK + 4 ms to ensure programming
mode can be entered.
In summary, more information on ATtiny15 Compatibility Mode can be found in sections “Port B (PB5:PB0)” on
page 2, “Internal PLL in ATtiny15 Compatibility Mode” on page 24, “8-bit Timer/Counter1 in ATtiny15 Mode” on
page 95, “Limitations of debugWIRE” on page 140, “Calibration Bytes” on page 150 and in table “Clock Prescaler
Select” on page 33.
6.2.4 Internal 128 kHz Oscillator
The 128 kHz internal Oscillator is a low power Oscillator providing a clock of 128 kHz. The frequency is nominal at
3V and 25C. This clock may be select as the system clock by programming the CKSEL Fuses to “0100”.
When this clock source is selected, start-up times are determined by the SUT Fuses as shown in Table 6-9.
Table 6-7. Start-up Times for Internal Calibrated RC Oscillator Clock
SUT[1:0]
Start-up Time
from Power-down
Additional Delay from
Reset (V
CC
= 5.0V) Recommended Usage
00 6 CK 14CK
(1)
BOD enabled
01 6 CK 14CK + 4 ms Fast rising power
10
(2)
6 CK 14CK + 64 ms Slowly rising power
11 Reserved
Table 6-8. Start-up Times for Internal Calibrated RC Oscillator Clock (in ATtiny15 Mode)
SUT[1:0]
Start-up Time
from Power-down
Additional Delay from
Reset (V
CC
= 5.0V) Recommended Usage
00 6 CK 14CK + 64 ms
01 6 CK 14CK + 64 ms
10 6 CK 14CK + 4 ms
11 1 CK 14CK
(1)
Table 6-9. Start-up Times for the 128 kHz Internal Oscillator
SUT[1:0]
Start-up Time from
Power-down
Additional Delay from
Reset Recommended Usage
00 6 CK 14CK
(1)
BOD enabled
01 6 CK 14CK + 4 ms Fast rising power
10 6 CK 14CK + 64 ms Slowly rising power
11 Reserved