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Ask an Expert Forum XTAL clock and 2A03
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  • nintendo entertainment system
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XTAL clock and 2A03

splatkillwill
splatkillwill over 5 years ago

I'm not sure where to ask this but I'm a newbie and I'm looking for someone to look over a schematic before I try it so I don't break anything (specifically a 2A03 (6502 based NES CPU) I only have one). The idea is to hook enough of it up to get it running and interact with it with a Adruino Uno. The Adruino only has enough pins to look at the lower 8 bits of the address bus but I figure when I get to the Adruino script I can just respond to the $fc and $fd of the $fffc and $fffd reset vector and not send any JMP instructions to anything lower that $ff00 to get started poking around.

image

I'm specifically worried about the XTAL clock. Its based on StandaloneNesPlayer (soniktech.com) but I don't have a 74HCT04N so I figured I'd use a transistor for the not gate but my R2 value of 10k is arbitrary.

image

I attached the Eagle project (I'm new at that too)

Attachments:
my_NES.zip
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  • michaelkellett
    michaelkellett over 5 years ago +3
    I don't think this oscillator will work. Use the recommended chip (or a ready made oscillator). BUT..... you seem to connecting the Arduino to the NES chip as if the Arduino were a memory device - what…
  • Jan Cumps
    Jan Cumps over 5 years ago in reply to splatkillwill +3
    The oscillator in the original article is a Pierce oscillator.
  • jc2048
    jc2048 over 5 years ago +3
    As Michael says, you'll find this tricky to get right without some way of looking at the waveform coming out. This worked with an ordinary 16MHz AT-cut processor crystal and a 2N3904 transistor. I've biased…
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  • splatkillwill
    splatkillwill over 5 years ago

    I ended up putting the xtal back on the original board and getting the clock off of there

    image

    I see some activity on the data and address buses but if I hard code a NOP its still seems random (with a NOP the address bus should steadily increment by one).

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  • splatkillwill
    splatkillwill over 5 years ago

    I ended up putting the xtal back on the original board and getting the clock off of there

    image

    I see some activity on the data and address buses but if I hard code a NOP its still seems random (with a NOP the address bus should steadily increment by one).

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  • michaelkellett
    michaelkellett over 5 years ago in reply to splatkillwill

    backcorp just posted a link to a project that might help you.

     

    https://www.youtube.com/watch?v=LnzuMJLZRdU

     

    MK

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