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Topic: set pins with shift and pin 13 for an ext. LED (Read 956 times) previous topic - next topic



These seem like newbie questions that were probably answered before at some point but I searched and couldn't find anything.

1.  Is there a way to set all 14 output pins, or better yet a subset of them, via a bit string.  Say I want to set all 14 HIGH.  Can I somehow use a shift or some other command to write 11111111111111 and set them all high, or set pin 4-7 high with 00001111000000?  Can I set every other pin high from pin 3-8 by using 101010 somehow?  You get the idea.

2.  Is there a way to disable the on-board LED so I can use pin 13 to drive an external LED?

Thanks as always.  The arduino is so cool, I have to ration my time w/it so I can function at work :)


Hey libhart,

Take a look at the tutorial I wrote, in the section called "A word about port registers in the Atmega8 microcontroller":



That's beautiful!  Exactly what I wanted to do.  Good points about the code not being portable though, I'll have to give it some thought.  In my case I've got to set a sequence of pins high or low and I think it'd almost be more understandable w/the bit string than to have multiple 'for' loops all in a row.  Thanks again.


Glad I double checked things on your tutorial.  Told me how to do what I wanted, but the example is a bit off.  In your setup function, you have the below.  The top two lines are correct, but then the bottom two lines are switched.  PORTB is 8-13, not 2-7, same switch for PORTD.  Thanks.

       // set pins 0 (serial transmit) and 2..7 as output,
       // but leave pin 1 (serial receive) as input
       // (otherwise serial port will stop working!) ...
       DDRD = B11111101;  // digital pins 7,6,5,4,3,2,1,0

       // set pins 8..13 as output...
       DDRB = B00111111;  // digital pins -,-,13,12,11,10,9,8

       // Turn off digital output pins 2..7 ...
       PORTB &= B00000011;   // turns off 2..7, but leaves pins 0 and 1 alone

       // Write simultaneously to pins 8..13...
       PORTD = B00111000;   // turns on 13,12,11; turns off 10,9,8

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