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Boarduino pins?
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Boarduino pins?

by aspro648 on Tue Feb 19, 2008 11:35 pm

OK, feeling really stupid. When I look at the Boarduino and see pin "D8" on the board, is that pin "8" for programming, or is it pin "14" (looking at schematic on


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by adafruit on Wed Feb 20, 2008 12:45 am

its the "arduino digital pin 8" as used in the arduino software, which is pin 14 on the atmega chip

its quite confusing!

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by aspro648 on Wed Feb 20, 2008 2:32 am

Thanks for the quick reply. I'm on tutorial 5, so hopefully that will help me understand. My poor old brain has lost some spring since my Sinclair ZX-81 days. I'm surprised I haven't let out any of the magic smoke of your Boarduino yet.

How about a tutorial #6 on analog inputs?

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by aspro648 on Fri Feb 22, 2008 3:33 pm

Let me see if I've come to the correct understanding of the Boarduino pins.

Digital pins (0-13) are accessed using digitalRead(), digitalWrite(), and analogWrite().

The analog pins (0-5) are accessed only using analogRead().

Clear as mud, eh?

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by darus67 on Fri Feb 22, 2008 4:20 pm

You're close.
Not all of the Digital I/O pins are capable of PWM (analog output).
Only pins 3, 5, 6, 9, 10, and 11 can provide PWM output.
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by jgotthardt on Sat Feb 23, 2008 8:12 am

Also, analog pins 0 thru 5 can be used as digital pins 14 thru 19.

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by mtbf0 on Sat Feb 23, 2008 1:10 pm

... and of course the real fun comes when you ditch the api and start reading the atmega168 datasheet. only then will you know true freedom.

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by caitsith2 on Sat Feb 23, 2008 8:26 pm

That whole analog pin/digital pins is really not too well documented, I do have to agree with that.

DigitalRead/DigitalWrite applies to 0-19 (20 I/O lines), PinMode is explicitly required for these calls.

AnalogRead applies to 0-5 (Which would be digital 14-19), no PinMode call required.

AnalogWrite applies to 3,5,6,9,10,11, (same mapping as the digital pins.) no PinMode call required. Using analogWrite on any of the other digital pins will digitalWrite a 1 if >127 or a 0 if <= 127, and the PinMode is still done for you.

Finally, if you don't mind diving a little deeper, like the data sheets, you can access more than one pin at the same time, both for reading, and writing.

Code: Select all | TOGGLE FULL SIZE
Example: a code snippet taken from one of my arduino projects, where I needed to read/write 8 pins as fast as possible.  This leaves DigitalRead/DigitalWrite/PinMode out of the question.

unsigned char readdata(unsigned char address)
  unsigned char data;

  DDRB = 0x0F;    //Data lines 0-1 from another device, are inputs.
                          // /WR, /RD, A0, A1 are outputs.
  DDRD &= ~0xFC;  //Data lines 2-7 from another device are outputs.
                             //TX/RX are left as they are.
  PORTB &= ~0x03;  //Clear A0/A1 value,
  PORTB |= (address & 0x03);  //And set it to the parameter.
  PORTB &= ~0x04;  // Activate /RD
  delayMicroseconds(1);  //Wait for data to be ready
  data=((PINB&0x30)>>4) | (PIND&0xFC);  //Now read the data

  PORTB |= 0x04;  //And deactivate /RD
  return data;

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