ATmega165 datasheet(281/336 Pages) ATMEL

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281

ATmega165/V

2573G–AVR–07/09

External Clock Drive

Waveforms

Figure 127. External Clock Drive Waveforms

External Clock Drive

Maximum speed vs. V

Maximum frequency is depending on V

CC. As shown in Figure 128 and Figure 129, the

Maximum Frequency vs. V

CC curve is linear between 1.8V < VCC < 4.5V. To calculate

the maximum frequency at a given voltage in this interval, use this equation:

To calculate required voltage for a given frequency, use this equation::

At 3 Volt, this gives:

Thus, when V

CC = 3V, maximum frequency will be 9.33 MHz.

At 6 MHz this gives:

Thus, a maximum frequency of 6 MHz requires V

CC = 2.25V.

VIL1

VIH1

Table 116. External Clock Drive

Symbol

Parameter

VCC=1.8-5.5V

VCC=2.7-5.5V

VCC=4.5-5.5V

Units

Min.

Max.

Min.

Max.

Min.

Max.

1/tCLCL

Oscillator

Frequency

MHz

tCLCL

Clock Period

1000

125

62.5

tCHCX

High Time

400

tCLCX

Low Time

400

tCLCH

Rise Time

2.0

1.6

0.5

μs

tCHCL

Fall Time

2.0

1.6

0.5

μs

Δt

CLCL

Change in period

from one clock

cycle to the next

Table 117. Constants used to calculate maximum speed vs. V

Voltage and Frequency range

2.7 < V

CC < 4.5 or 8 < Frq < 16

8/1.8

1.8/8

2.7

1.8 < V

CC < 2.7 or 4 < Frq < 8

1.8

Frequency

V Vx

–

()

•

Voltage

F Fy

–

()

•

Frequency

1.8

--------

32.7

–

()

•

9.33

Voltage

1.8

--------

–

()

•

1.8

2.25

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