Datasheet

175
8183F–AVR–06/12
ATtiny24A/44A/84A
20.4 Clock Characteristics
20.4.1 Accuracy of Calibrated Internal Oscillator
It is possible to manually calibrate the internal oscillator to be more accurate than default factory
calibration. Note that the oscillator frequency depends on temperature and voltage. Voltage and
temperature characteristics can be found in Figure 21-109 on page 237 and Figure 21-110 on
page 238.
Notes: 1. Accuracy of oscillator frequency at calibration point (fixed temperature and fixed voltage).
20.4.2 External Clock Drive
Figure 20-2. External Clock Drive Waveform
Table 20-2. Calibration Accuracy of Internal RC Oscillator
Calibration
Method Target Frequency V
CC
Temperature
Accuracy at given voltage
& temperature
(1)
Factory
Calibration
8.0 MHz 3V 25°C±10%
User
Calibration
Fixed frequency within:
7.3 – 8.1 MHz
Fixed voltage within:
1.8V – 5.5V
Fixed temperature
within:
-40°C to +85°C
±1%
V
IL1
V
IH1
Table 20-3. 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
Δt
CLCL
Change in period from one clock cycle to the next 2 2 2 %