Datasheet

164
ATtiny25/45/85 [DATASHEET]
2586Q–AVR–08/2013
21.4 Clock Characteristics
21.4.1 Calibrated Internal RC Oscillator Accuracy
It is possible to manually calibrate the internal oscillator to be more accurate than default factory calibration. Please
note that the oscillator frequency depends on temperature and voltage. Voltage and temperature characteristics
can be found in Figure 22-40 on page 193 and Figure 22-41 on page 193.
Notes: 1. Accuracy of oscillator frequency at calibration point (fixed temperature and fixed voltage).
2. ATtiny25/V, only: 6.4 MHz in ATtiny15 Compatibility Mode.
3. Voltage range for ATtiny25V/45V/85V.
4. Voltage range for ATtiny25/45/85.
21.4.2 External Clock Drive
Figure 21-3. External Clock Drive Waveforms
Table 21-2. Calibration Accuracy of Internal RC Oscillator
Calibration
Method Target Frequency V
CC
Temperature
Accuracy at given Voltage
& Temperature
(1)
Factory
Calibration
8.0 MHz
(2)
3V 2510%
User
Calibration
Fixed frequency within:
6 – 8 MHz
Fixed voltage within:
1.8V - 5.5V
(3)
2.7V - 5.5V
(4)
Fixed temperature
within:
-40C to +85C
±1%
V
IL1
V
IH1
Table 21-3. External Clock Drive Characteristics
Symbol Parameter
V
CC
= 1.8 - 5.5V V
CC
= 2.7 - 5.5V V
CC
= 4.5 - 5.5V
UnitsMin. Max. Min. Max. Min. Max.
1/t
CLCL
Clock Frequency 0 4 0 10 0 20 MHz
t
CLCL
Clock Period 250 100 50 ns
t
CHCX
High Time 100 40 20 ns
t
CLCX
Low Time 100 40 20 ns
t
CLCH
Rise Time 2.0 1.6 0.5 µs
t
CHCL
Fall Time 2.0 1.6 0.5 µs
t
CLCL
Change in period from one clock cycle to the next 2 2 2 %