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DIFFERENCE SPEED PORTC VS PORTB ATMEGA644P

 
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benoit

Bascom Member



Joined: 24 Jul 2007
Posts: 177

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PostPosted: Thu Jun 07, 2018 6:36 am    Post subject: DIFFERENCE SPEED PORTC VS PORTB ATMEGA644P Reply with quote

HELLO


I FOUND THAT THERE IS A DIFFERENCE SPEED BETWEEN PORTC AND PORT B

atmega644p

voltage vcc 5v25 (under dont start) current consumption >100ma

first of all clock at 40mhz with external clock fuze 010000

program in basic (may be in asm it is faster)

do
portc=0
portc=255
loop

speed mesured at oscilloscop 2.69mhz the same for porta and portd

do
portb=0
portb=255
loop

speed mesured at oscilloscop 5.76mhz

the frequency is stable in all case

WHY THIS DIFFERENCE ?

(BASCOM-AVR version : 2.0.7.3 , Latest : 2.0.8.1 )
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laborratte

Bascom Expert



Joined: 27 Jul 2005
Posts: 262
Location: Berlin

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PostPosted: Thu Jun 07, 2018 2:22 pm    Post subject: Reply with quote

You really wonder that the chip does weird things when you run it way outside its specifications?
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benoit

Bascom Member



Joined: 24 Jul 2007
Posts: 177

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PostPosted: Sun Jun 10, 2018 3:26 pm    Post subject: Reply with quote

HELLO

IF I DISABLE INTERRUPT ALL THE PORTS RUN AT SAME FREQUENCY LET 5.76MHZ
LET ABOUT 11MHZ BY BYTES
GOOD
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