Shop OBEX P1 Docs P2 Docs Learn Events
What should RTCC be tied to when unused? — Parallax Forums

What should RTCC be tied to when unused?

Jim PalmerJim Palmer Posts: 23
edited 2005-02-26 22:19 in General Discussion
Hi All,

I'm trying to determine whether the RTCC pin should be tied to Vss or Vdd when it is not used for external triggering. I looked through www.sxlist.com/techref/logic/xtrapins.htm, but I could not find an explicit reference to RTCC (though, it also didn't explicitly say anything about RB1 either). Should it be treated like any other input?

Opinions?

Thanks,

Jim

Comments

  • KenMKenM Posts: 657
    edited 2005-02-25 22:39
    Hi Jim,

    Your post was viewd many times but no replies....so here is my·useless input.

    I have never had a project yet that uses RTCC, and to that end I have always left the pin open. I don't know if it is subjected to the same problems that occur by leaving unused input pins open.

    To the best of my knowledge, leaving RTCC 'floating' has not caused any trouble.

    For unused inputs (RB.X, ETC), I always make them an output and then drive the the unused pin low, but I think most use a pull up resistor of 10k or so on unused pins.

    In my applications I am not concerned about the possibility of a short to power on the unused pins configured as outputs and driven low.

    $0.02

    k

    I am coming back to Los Angeles today after 5 weeks in Japan....yahoo· <end rave>
  • Paul BakerPaul Baker Posts: 6,351
    edited 2005-02-26 14:46
    I had the same question a couple weeks ago when finalizing my PCB, I ended up running ground to it. I will be powering up the board today, I let you know if I see sparks eminating from the RTCC pin [noparse]:)[/noparse]
  • BeanBean Posts: 8,129
    edited 2005-02-26 16:30
    I also always left the RTCC pin open, but I think grounding it is a good idea. I just tried it on my board will no ill effects.
    Bean.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Check out· the "SX-Video Display Module"

    www.sxvm.com
    ·
  • Guenther DaubachGuenther Daubach Posts: 1,321
    edited 2005-02-26 22:19
    Maybe, this is just a question of "gusto" - I usually pull it up to Vdd via a 4k7 resistor.

    I think "Grounding" it, or pulling it up to Vdd are both fine but you should not leave it unconnected as floating inputs can always cause unpredictable results.

    Imagine what could happen in an "ISR-less" application when you have set bit 5 in the OPTION register by some reason, and the floating RTCC input causes the RTCC to be incremented causing a jump to $000 when it overflows. As your program does not contain ISR code, it may restart, or do some other crazy things.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Greetings from Germany,

    G
Sign In or Register to comment.