Digital-Out 13 / "14 to 19"

Two short questions, maybe anyone can help…

  1. Are there any restrictions in using Digital Out 13, as there is built-in resitor for LEDs, or can it be used for software generated PWM for instance as any other Digital Out? In other words: is the voltage here too low here for some applications?

  2. I saw on that Analog In 0 and 1 can be used as Digital Out 14 and 15.
    → Seems to work for all Analog Ins as Digital Out 14-19 on my Arduino NG with the arduino-0008!
    2a) Is this a hidden function due to the design of the ATmega-168? If yes, will is it (elecrically and so on) save to use?
    2b) Will it be supported in future versions of the Arduino-board?

Maybe someone of the Arduino-Team can answer the “2b)” question? Thanx!

On the ATmega168 (and the ATmega8), the analog input pins can be used as normal digital i/o pins (except for analog inputs 6 and 7 on the surface mount versions of the ATmega168 on, for example, the Arduino Mini). We’ll probably retain “hidden” support in the software for using these as digital pins 14-19, but if not, you could still read from the PORTC register directly.

Be careful with digital 13. It gets strobed by the bootloader. The resistor will keep you from driving large loads, but you can use it as an input or a logic level output. You just won’t get more than a few milliamps through it.

Thank you very much jims and mellis for the quick and very helpful replies!

@mellis: I think it would be a good idea to keep up the support for PINS 14-19 in the arduino(wiring) language.
For my current project for instance I do not need analogue ins, as I am using MIDI to drive my servos and LEDs.
In another thread ( there is btw a hint how to switch serial ports to have at least 13 digital out.

→ So maybe this hidden feature (using analogue-in as digital in/OUT) should even become an offical one in the future???

PS: I’m using my arduinos for only 3 weeks now - and having so much fun, the Hardware, the Software and the discussions going on in the web (espacially at… of course) are just great!