DIFFERENCE SPEED PORTC VS PORTB ATMEGA644P

benoit · Joined: 24 Jul 2007 Posts: 177

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 )

laborratte · Joined: 27 Jul 2005 Posts: 299 Location: Berlin

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

benoit · Joined: 24 Jul 2007 Posts: 177

HELLO

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