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8127B–AVR–08/09
16.4 Clock Characteristics
16.4.1 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 17-39 on page 142 and Figure 17-40 on
page 142.
Notes: 1. Accuracy of oscillator frequency at calibration point (fixed temperature and fixed voltage).
16.4.2 External Clock Drive
Figure 16-2. External Clock Drive Waveform
Table 16-2. 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 temp. within:
-40°C – 85°C
±1%
Table 16-3. 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 %
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