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Re: Cosmac Elf on breadboard troubles

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  • alkopop79
    Is it a good idea to ground all the floating pins?
    Message 1 of 51 , Mar 3, 2012
      Is it a good idea to ground all the floating pins?

      --- In cosmacelf@yahoogroups.com, "Al" <wa9hsl@...> wrote:
      >
      > Your latest description might suggest an open or floating input. That could easily happen with a temporary breadboard arrangement like that, especially if it has been used a good deal. Aside from that I couldn't troubleshoot the pictured board even if I were sober... :o)
      > Good luck with it though.
      >
      > al
      > ....
      >
      >
      > --- In cosmacelf@yahoogroups.com, "alkopop79" <alkopop79@> wrote:
      > >
      > > ...and there's a photo here:
      > >
      > > http://flic.kr/p/bnaLoQ
      > >
      > >
      > >
      > > --- In cosmacelf@yahoogroups.com, "alkopop79" <alkopop79@> wrote:
      > > >
      > > > The schematics:
      > > >
      > > > http://www.incolor.com/bill_r/elf/html/elf-1-35.htm
      > > >
      > > > --- In cosmacelf@yahoogroups.com, bill rowe <bill_rowe_ottawa@> wrote:
      > > > >
      > > > >
      > > > > I'm sure somebody will find it but you should post a picture and schematic.
      > > > > To: cosmacelf@yahoogroups.com
      > > > > From: alkopop79@
      > > > > Date: Thu, 1 Mar 2012 14:36:48 +0000
      > > > > Subject: [cosmacelf] Cosmac Elf on breadboard troubles
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      > > > > Hi all,
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      > > > > I've been trying to build a Cosmac Elf on breadboard using the original Poular Science article but the 4016s (quad bilateral switches) just don't work. The strange thing is that I checked them and tested them millions of times, even bought new ones. Yet, when I place them in the circuitry, they cease to let any signal pass. It's driving me nuts. This is what I have done so far:
      > > > >
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      > > > >
      > > > > - checked 4016s on a separate breadboard. When ENABLE pins are set HIGH and an input pin is HIGH, the output will be HIGH, too. If ENABLE is LOW, nothing goes through. They work perfectly when tested on a different breadboard.
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      > > > > - forced enable an all pins by attaching them to the positive voltage supply. Normally that enables the switches. Didn't help,
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      > > > > - if I set the output pins that go to 4050 (or the input pins of 4050) HIGH, the hex display shows '1' ,'2','4' or '8' depending on which pin. I assume that means the 4050s and the hex displays work. Also, when powered up and in RUN mode, the hex displays show 'FF'. When set to LOAD mode, the displays show '00'. I assume that means the control circuit and the outputs work.
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      > > > > - rebuilt the entire input and output section.
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      > > > > I think I have run out of ideas. The perfectly working 4016s cease to work in the circuit, even if I rebuilt everything. Any ideas would be appreciated!
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      > > > > Greg
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    • David W. Schultz
      ... Those pins are connected to /MREAD and /MWR. When you request a DMA-IN cycle you get a memory write cycle where your peripheral must provide the data.
      Message 51 of 51 , Mar 17, 2012
        On 03/17/2012 10:49 AM, alkopop79 wrote:
        > Can you guys tell me what should be the state
        > of pins 18 and 20 (output disable and write enable) in run and load
        > mode and when pressing the input button? The datasheet doesn't have
        > much info on this.

        Those pins are connected to /MREAD and /MWR. When you request a DMA-IN
        cycle you get a memory write cycle where your peripheral must provide
        the data. (machine cycle type no. 7 in the 1802 data sheet, ca. 1979)



        --
        David W. Schultz
        http://home.earthlink.net/~david.schultz
        "Who? What? Where? When? Aahhhg!" - Duck Dodgers
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