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using a 6522 with a 6802

Discussion in 'General Electronics' started by Lee K. Gleason, Feb 9, 2008.

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  1. I'm trying to put together a small controller, using a Motorola 6802 (more
    or less, a 6800 with some onboard RAM), a 27C512 EPROM, and a 6522 VIA (you
    know, old school, circa 1980 style). It's designed in the simplest way
    possible, simple chip select, oscillator chip clock, really nothing
    complicated about it. I'm having trouble getting it to work though. All the
    signals look right, but the 6522 never does anything. I'm wondering if just
    connecting the E clock output from the 6802 to the 6522 CLK is causing any
    problems, or if more elaborate handling of the timing is necessary. Anyone
    out there ever use a 6522 in a 6800 environment successfully? Any tricks to
  2. Tom2000

    Tom2000 Guest

    Wow, a blast from the past.

    I've done it, but that was over 20 years ago, and certainly don't
    remember exactly how. Hanigng a 6522 on the Motorola bus isn't
    difficult, though. I'd suggest that you carefully read the data
    sheets for both chips, paying particular attention to the clock phase,
    R/W, and chip select conditions. You'll find your solution there.

    If you still have trouble, switch to a 6502 processor. If you can
    find one. :)

    Good luck!

  3. Jakthehammer

    Jakthehammer Guest

    Time to use ICE....Heehee.......
  4. Steve

    Steve Guest

    I've used that combination successfully. The 6522 was a much better UART
    than the Motorola part was. But unfortunately, it was so long ago that I
    can't remember how the clocking was done. I doubt it was much external
    logic - we didn't use much more than PAL's in those days. Check to see if
    its clock needs to be inverted relative to the 6802 to align the Rd/Wr or CS
    edges where they need to be. I think clock phase was one of the differences
    between the 6502 and 6802 processors.

    I'm curious as to why you would not just use one of the thousands of
    available Flash based microcontrollers for your project. They cost less,
    there are less obsolescence issues, and all the hardware is already debugged
    for you. Most have serial emulation available for under $100. I loved the
    6809 in its day, but its just been overshadowed in speed, size and cost. If
    your software is expected to have any complexity at all, don't underestimate
    the difficulties of debugging without emulation. It takes 10 times longer
    than it will with even the simplest emulation tools.

    Good luck with your project,
  5. Jim

    Jim Guest

    I just looked at some old notes that I had - using a 68HC11 and a 6522.
    It looks like I ran the E line directly into ph2 (pin 25) - no special
    buffering at all. I put A12 into CS1 and then used a 74hc139 to decode
    A13-A14-A15 into CS2. Note that CS2 is inverted so is active low. IRQ,
    and R/W run straight in. If you're careful with your connections, it
    should work (I know that board is still around here somewhere - it
    worked well for many years for me).

  6. Rich Grise

    Rich Grise Guest

  7. Thanks all for the info. I'm doing this out of nostalgia - when 6800s were
    new, I was too busy and too hardware-ignorant to experiment with them. Now,
    I've got some spare time, and a lot more expereince under my belt, so I'm
    revisiting the chips I missed out on back then..
  8. Tim Williams

    Tim Williams Guest

  9. Tom2000

    Tom2000 Guest

  10. Tom2000

    Tom2000 Guest

  11. Tom2000

    Tom2000 Guest

  12. Tom2000

    Tom2000 Guest

    Well, Lee, if it's about nostalgia, then all is forgiven. :) I can
    certainly understand your motivation, and it's a good one. (I just
    received an HP-11C calculator that I purchased on eBay for nothing
    more than nostalgia.)

    FWIW, I used a 6802 for the first computer that I "designed" and built
    from scratch.

    I wire wrapped it, and wrote my own monitor by hand-assembling the
    code, then punching it into a borrowed EPROM programmer by hand. It
    took quite a few tries since debugging involved punching another

    I had a lot of fun with that project, and really learned a bunch.

    Enjoy your project. I know you're having fun.

    Very 73,

    Tom AB9B
  13. Steve

    Steve Guest

    Nothing wrong with having fun....

    Compared with Intel micros, the Motorola parts were wonderful for assembly
    language: regular architectures, CC flags that were consistent regardless of
    the op code, and few special purpose registers. When the 6809 came out, it
    fixed the biggest 6802 flaw IMO - a single index register with limited
    addressing modes.

    I'm surprised you can still buy the parts.

    Good luck
  14. Phil Hobbs

    Phil Hobbs Guest

    Sure--such as any balanced and detailed discussion of controversial issues.


    Phil Hobbs
  15. neon


    Oct 21, 2006
    you should not mix differnent family and expect it to work even logicaly the are the same
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