Datasheet

306
2545T–AVR–05/11
ATmega48/88/168
29.4 Clock characteristics
29.4.1 Calibrated internal RC oscillator accuracy
Notes: 1. Voltage range for Atmel ATmega48V/88V/168V.
2. Voltage range for Atmel ATmega48/88/168.
29.4.2 External clock drive waveforms
Figure 29-3. External clock drive waveforms.
29.4.3 External clock drive
Table 29-1. 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 29-2. 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
04010020MHz
t
CLCL
Clock period 250 100 50
nst
CHCX
High time 100 40 20
t
CLCX
Low time 100 40 20
t
CLCH
Rise time 2.0 1.6 0.5
μs
t
CHCL
Fall time 2.0 1.6 0.5
Δt
CLCL
Change in period
from one clock
cycle to the next
22 2%