Datasheet

Figure 29-1. Maximum Frequency vs. V
CC
4MHz
1.8V 2.7V 4.5V
10MHz
20MHz
5.5V
Safe Operating Area
29.4. Clock Characteristics
Related Links
Calibrated Internal RC Oscillator on page 48
29.4.1. Clock characteristics
Table 29-4. Calibration accuracy of internal RC oscillator.
Frequency V
CC
Temperature Calibration accuracy
Factory calibration 8.0MHz 3V 25°C ±10%
User calibration 7.3 - 8.1MHz 1.8 - 5.5V -40°C - 85°C ±1%
29.4.2. External Clock Drive Waveforms
Figure 29-2. External Clock Drive Waveforms
V
IL1
V
IH1
29.4.3. External Clock Drive
Table 29-5. External Clock Drive
Symbol Parameter V
CC
= 1.8 - 5.5V V
CC
= 2.7 - 5.5V V
CC
= 4.5 - 5.5V Units
Min. Max. Min. Max. Min. Max.
1/t
CLCL
Oscillator 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
Atmel ATmega644A [DATASHEET]
Atmel-42716C-ATmega644A_Datasheet_Complete-10/2016
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