Difference between digitalRead and PORTD read?

Projects Programming
1

#define LineAIn 6
#define LineBIn 3

pinMode(LineAIn,INPUT_PULLUP);
pinMode(LineBIn,INPUT_PULLUP);

The following two statements do not work the same. Can someone tell me why?

while(digitalRead(LineAIn)&&digitalRead(LineBIn));

while(PORTD&B01001000==B01001000);

Regards,

Bert

2

Homework? Quiz? Test?

4

The Arduino functions read one pin at a time so the two pins might be sampled several microseconds apart. PORTD reads all 8 pins at the same time. Is that important?

5

Not a test or quiz. This is a real problem.

if would have thought that this statement

while(PORTD&B01001000==B01001000);

would cause the micro to loop there until one of the pins goes low then process the next statement.

This code works:

while(digitalRead(LineAIn)&&digitalRead(LineBIn));

but this code does not wait for one of the lines (pin 6 or pin 3) to drop low:

while(PORTD&B01001000==B01001000);

it goes directly to the next statement.

I'm trying to get this code to run as fast as possible and testing using digitalRead is very slow.

Regards,

Bert

6

Use an extra set of ().

The code (probably) compares the first B01001000 with the second B01001000, it does not compare the result of the & operation with the second B01001000.

Try

while((PORTD&B01001000)==B01001000);
8

Works better if you read PIND instead of PORTD.

9

The fact == binds tighter than & and | is a constant source of annoyance in C, its just counter-intuitive and
wrong, but we have to live with it...

10

Hi All,

The statement:

while((PORTD&B01001000)==B01001000); did not work properly but the statement:

while((PIND&B01001000)==B01001000); did work.

Thank you all for your suggestions.

Regards,

Bert

11

bvdb:
Hi All,

The statement:

while((PORTD&B01001000)==B01001000); did not work properly but the statement:

while((PIND&B01001000)==B01001000); did work.

Thank you all for your suggestions.

Regards,

Bert

Do you understand the difference between an output register (PORT) and an input register (PIN)?