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Re: [softrock40] 12F683 Question

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  • brainerd@wildblue.net
    ... I don t know if the 12F683 has internal pull-ups. If so, then a single wafer switching between ground and open will suffice. Generally with CMOS, an open
    Message 1 of 13 , Jul 2, 2008
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      On 2 Jul 2008 at 7:20, Pete Smith wrote:

      > Good question - I am rethinking that, given that I have a separate switch
      > wafer dedicated to frequency control, and another for switching the
      > BPFs. Maybe I can dispense with the diodes on both of those functions. I
      > was thinking by analogy to a band decoder, where the same outputs must be
      > shared between different sets of choices (like 4 antennas and 6 BPFs).
      >
      > 73, Pete
      >
      I don't know if the 12F683 has internal pull-ups. If so, then a single wafer switching between
      ground and open will suffice. Generally with CMOS, an open input is undefined, so it must
      either be pulled up to Vcc or down to ground at all times. The only issue in connecting to
      ground is making sure the pin cannot be an output when it is connected to ground.

      Dave - WB6DHW
      <http://wb6dhw.com>
    • Pete Smith
      Well, connecting to ground is exactly what the DIP switch on the 8.3 Xtall board does. It has pull-ups and also series protective resistors against the kind
      Message 2 of 13 , Jul 3, 2008
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        Well, connecting to ground is exactly what the DIP switch on the 8.3 Xtall
        board does. It has pull-ups and also series protective resistors against
        the kind of unintentional output scenario you describe. Seems like a good
        design.

        On another subject, after thinking a bit more, I will still need the
        steering diodes to keep from unintentionally tying input lines together,
        because of the different combinations needed for the 6 center frequencies
        of interest.

        73, Pete N4ZR

        At 11:21 AM 7/2/2008, brainerd@... wrote:
        >On 2 Jul 2008 at 7:20, Pete Smith wrote:
        >
        > > Good question - I am rethinking that, given that I have a separate switch
        > > wafer dedicated to frequency control, and another for switching the
        > > BPFs. Maybe I can dispense with the diodes on both of those functions. I
        > > was thinking by analogy to a band decoder, where the same outputs must be
        > > shared between different sets of choices (like 4 antennas and 6 BPFs).
        > >
        > > 73, Pete
        > >
        > I don't know if the 12F683 has internal pull-ups. If so, then a single
        > wafer switching between
        >ground and open will suffice. Generally with CMOS, an open input is
        >undefined, so it must
        >either be pulled up to Vcc or down to ground at all times. The only issue
        >in connecting to
        >ground is making sure the pin cannot be an output when it is connected to
        >ground.
        >
        >Dave - WB6DHW
        ><http://wb6dhw.com>
        >
        >
        >------------------------------------
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