31.3 Clock Characteristics
31.3.1
Calibrated Internal RC Oscillator Accuracy
Table 31-1. Calibration Accuracy of Internal RC Oscillator
Frequency
VCC
Temperature
Calibration Accuracy
Factory Calibration
User Calibration
8.0 MHz
3V
25°C
10%
1.8V - 5.5V(1)
2.7V - 5.5V(2)
7.3 - 8.1 MHz
-40°C - 85°C
1%
Notes: 1. Voltage range for ATmega640V/1281V/1280V/2561V/2560V.
2. Voltage range for ATmega640/1281/1280/2561/2560.
31.3.2
External Clock Drive Waveforms
Figure 31-5. External Clock Drive Waveforms
VIH1
VIL1
31.4 External Clock Drive
Table 31-2. External Clock Drive
VCC=1.8-5.5V
VCC=2.7-5.5V
VCC=4.5-5.5V
Symbol
Parameter
Min.
Max.
Min.
Max.
Min.
Max.
Units
Oscillator
Frequency
1/tCLCL
0
2
0
8
0
16
MHz
tCLCL
tCHCX
tCLCX
tCLCH
tCHCL
Clock Period
High Time
Low Time
Rise Time
Fall Time
500
200
200
125
50
62.5
25
ns
ns
ns
μs
μs
50
25
2.0
2.0
1.6
1.6
0.5
0.5
Change in period
from one clock
cycle to the next
ΔtCLCL
2
2
2
%
374
ATmega640/1280/1281/2560/2561
2549L–AVR–08/07
ATMEL [ ATMEL ]
