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15210Re: First ELF project

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  • joshbensadon
    Aug 6, 2014
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      Hi Jon,

      An oscillator can will work fine, the 1802 isn't fussy.  Pump it into pin 1, clk, ignore pin 39.
      Those can's produce a nice square wave!

      If you look at the VELF a little closer, you will see that the EPROM starts at 0000-7FFF then gets remapped to 8000-FFFF on the first occurrence of A15 going high.  It's first instruction is then a long jump to 8003, the next instruction fetch remaps the EPROM and lets the RAM operate at 0000-7FFF.  If you flip the mode switch to ELF, it simply forces the EPROM to be at 8000-FFFF and keeps RAM in the lower 32K.  In this mode, you can just toggle in C0 80 00 to go into the monitor.

      But, I totally agree with your original plan.  Build the basic ELF, and then start modifying it.  I will recommend 2 options.  1. Either do it on a large perfboard for expansion or 2. Do it on one of those perfboards with a card edge connector, then build a mother board so you can plug in other boards to your system as it grows.

      Cheers,
      Josh
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