ATMEGA640 datasheet(165/436 Pages) MICROCHIP

부품명	ATMEGA640

상세설명	8-bit Microcontroller with 16/32/64KB In-System Programmable Flash

PDF	436 Pages

Scroll/Zoom	100%

제조업체	MICROCHIP [Microchip Technology]

홈페이지	http://www.microchip.com

Logo

165 / 436 page

165

ATmega640/V-1280/V-1281/V-2560/V-2561/V [DATASHEET]

DS40002211A

Each half period of the external clock applied must be longer than one system clock cycle to ensure correct sam-

pling. The external clock must be guaranteed to have less than half the system clock frequency (fExtClk < fclk_I/O/2)

given a 50/50% duty cycle. Since the edge detector uses sampling, the maximum frequency of an external clock it

can detect is half the sampling frequency (Nyquist sampling theorem). However, due to variation of the system

clock frequency and duty cycle caused by Oscillator source (crystal, resonator, and capacitors) tolerances, it is rec-

ommended that maximum frequency of an external clock source is less than fclk_I/O/2.5.

An external clock source can not be prescaled.

Figure 18-2. Prescaler for synchronous Timer/Counters

PSR10

Clear

clk

I/O

Synchronization

TIMER/COUNTERn CLOCK SOURCE

clk

TIMER/COUNTERn CLOCK SOURCE

clk

CSn0

CSn1

CSn2

CSn0

CSn1

CSn2

ATMEGA640 데이터시트(PDF) 165 Page - Microchip Technology