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5156Is there a Hex Keypad standard?

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  • ted_rossin
    Feb 1, 2007
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      I built an Elf from the Popular Electronics 1976 article back in
      1978 and around 1979 I added a hex key pad in place of the binary
      interface (I used a solderless breadboard instead of the 8 switches
      for cost reasons).


      Click on the picture for a larger view.

      My keypad is getting flakey and I'm thinking about a redesign and
      thought that if there is a standard then I should adhere to that.
      The following is a description of how my current keypad behaves.

      My keypad drives the INPUT switch after every 2nd key press. This
      also drives /EF4 and /DMA_IN low and drives 8-bit data onto the data
      bus in response to the ELF doing a Port 4 read. I think the INPUT
      to /EF4 and /DMA_IN and port 4 read is standard ELF behavior when
      the machine is in the LOAD state.

      I also have my keypad drive /EF3 low when any key is pressed
      and /EF4 low when the LOAD button is pressed. I have a toggle
      switch that selects between the LOAD button and the auto-load on
      every 2nd key press.

      This is my main user interface. Basically, I can look for EF3
      active and then read port 4 to see which key is pressed under
      program control or use the thing in auto-load mode to load programs
      starting at location zero. The later is how I jump to my monitor
      code that is held in ROM at location 0xf000.

      The keypad also has 8 LEDs connected to PORT 4 as I could not afford
      the HP hex displays back then.
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