Datasheet

371
2549O–AVR–05/12
ATmega640/1280/1281/2560/2561
31.3 Clock Characteristics
31.3.1 Calibrated Internal RC Oscillator Accuracy
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
31.4 External Clock Drive
Table 31-1. Calibration Accuracy of Internal RC Oscillator
Frequency V
CC
Temperature Calibration Accuracy
Factory Calibration 8.0MHz 3V 25C±10%
User Calibration 7.3MHz - 8.1MHz
1.8V - 5.5V
(1)
2.7V - 5.5V
(2)
-40C - 85C±1%
V
IL1
V
IH1
Table 31-2. External Clock Drive
Symbol Parameter
V
CC
= 1.8V - 5.5V V
CC
= 2.7V - 5.5V V
CC
= 4.5V - 5.5V
UnitsMin. Max. Min. Max. Min. Max.
1/t
CLCL
Oscillator
Frequency
0208016MHz
t
CLCL
Clock Period 500 125 62.5
nst
CHCX
High Time 200 50 25
t
CLCX
Low Time 200 50 25
t
CLCH
Rise Time 2.0 1.6 0.5
s
t
CHCL
Fall Time 2.0 1.6 0.5
t
CLCL
Change in period
from one clock
cycle to the next
22 2%