6674Re: [cosmacelf] Re: Free Running .pdf
- Apr 5, 2010RickC wrote:
> At this stage I just want to see if the CPU works!<grin>I suggest getting one of those white plastic solderless breadboarding
sockets. Plug the 1802 into it. Wire the lines shown on that "1802 free
running" high through pullup resistors to +V (resistor value doesn't
Power supply: Anything from 3v to 6v is fine. Two AA batteries is
simple. Put a flashlight bulb in series as a current limiter. If you
short something or connect power backwards by mistake, it will light and
prevent any damage.
Oscillator: The simplest scheme is to connect a 1 megohm or greater
value resistor between 1802 pins 1 and 39. Then stick your finger or a
long piece of wire on pin 1 to pick up random 60 Hz noise. This is
enough to clock the 1802. :-)
Move the resistor on the DMA-OUT pin so it goes to ground instead of +v.
This tells the 1802 to start doing DMA-OUT (memory read) cycles. An LED
with a resistor in series will serve as a "logic probe". You can probe
the address pins, and will see them toggling high/low like an 8-bit counter.
Wire up your 6810 RAM. Now when you do these DMA-OUT cycles, they will
be reading random data from the RAM, which you can see on the data bus.
You can build up your Elf like this, one chip at a time, wiring and
testing each one as you go.
Lee A. Hart | Ring the bells that still can ring
814 8th Ave N | Forget the perfect offering
Sartell MN 56377 | There is a crack in everything
leeahart earthlink.net | That's how the light gets in -- Leonard Cohen
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