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6802 clock

Discussion in 'General Electronics' started by Lee K. Gleason, Jul 22, 2005.

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  1. I'm building a simple 6802 single board system. I want to drive the CPU
    with an external oscillator, rather than using a crystal (got lots of 4 pin
    oscillators, not so many crystals). When using a crystal, the frequency of
    the crystal gets divided down by 4 by an internal part of the processor (so
    you use a 4 MHz crystal for a 1MHz clock).

    When using an external oscillator, like I want to do, does the same divide
    by 4 occur? That is, should I use a 4 MHz external oscillator, or a 1 MHz
    oscillator for a 1 MHz system clock?

    Lee K. Gleason N5ZMR
    Control-G Consultants
     
  2. John Fields

    John Fields Guest

     
  3. Bozzion

    Bozzion Guest

    why not? isn't the devider on chip?
     
  4. Frank

    Frank Guest

    By the way who makes the 6802, is Motorola still around?

    I'm building a simple 6802 single board system. I want to drive the CPU
    with an external oscillator, rather than using a crystal (got lots of 4 pin
    oscillators, not so many crystals). When using a crystal, the frequency of
    the crystal gets divided down by 4 by an internal part of the processor (so
    you use a 4 MHz crystal for a 1MHz clock).

    When using an external oscillator, like I want to do, does the same divide
    by 4 occur? That is, should I use a 4 MHz external oscillator, or a 1 MHz
    oscillator for a 1 MHz system clock?

    Lee K. Gleason N5ZMR
    Control-G Consultants
     
  5. John Fields

    John Fields Guest

    ---
    Motorola spun off their µC product line to Freescale Semiconductor,
    but I don't think you're going to find much 6802 around, since it's
    been obsolete for a while.

    Freescale suggests Rochester Electronics as a possible source, and
    Google will give you lots of hits. If what you're doing is new, why
    do you want to use a 6802 anyway?

    If you choose to reply, it's considered, in this group, to be
    courteous if you bottom post.
     
  6. Frank

    Frank Guest

    No I was just asking?
    Motorola came up with a good range of micro, I went to a few of there
    seminars, back in the 70's


    ---
    Motorola spun off their µC product line to Freescale Semiconductor,
    but I don't think you're going to find much 6802 around, since it's
    been obsolete for a while.

    Freescale suggests Rochester Electronics as a possible source, and
    Google will give you lots of hits. If what you're doing is new, why
    do you want to use a 6802 anyway?

    If you choose to reply, it's considered, in this group, to be
    courteous if you bottom post.
     
  7. Karl Uppiano

    Karl Uppiano Guest

    Sometimes a good 8-bit 1 MHz processor is all you need.
     
  8. John Fields

    John Fields Guest

    ---
    Yes, but that's not the point, which is that the 6802 is obsolete and
    only available from "surplus" dealers.

    For a desperate one-off, that might be OK, but going through the
    expense and hassle of stepping back in time when _many_ good 8 bit µC
    are available for cheap in the present hardly makes the exercise seem
    worth while.
     
  9. Rich Grise

    Rich Grise Guest

    John is absolutely right. For the effort it would take to track down
    data sheets and crap on that old of a part simply doesn't make any
    sense. I did a quick google on "6802 data sheet", without the quotes,
    and out of thousands of answers, none of them was about the old Moto
    micro. Heck, I saw a Basic Stamp Development Kit in Fry's not too
    long ago, for about a hundred and twenty-five bucks.

    What country are you in?

    Good Luck!
    Rich
     
  10. James Sweet

    James Sweet Guest


    Quite a few people build things using obsolete microcontrollers just because
    they can, I agree that if this is a production device then there's better
    choices, but if just fooling around or making something nostalgic then go
    for it.
     
  11. Karl Uppiano

    Karl Uppiano Guest

    I have brand new stuff in my junk box that has been obsolete for decades. If
    I have it, I'll use it, if only out of a sense of frugality. If I were
    building a commercial product, then availability would definitely be a
    primary consideration.
     
  12. Jim Adney

    Jim Adney Guest

    Gee, John, just being difficult, or trying to start a war?

    -
     
  13. John Fields

    John Fields Guest

     
  14. james

    james Guest

    A 6802 is essentially a MC6800, MC6875 and a MC6810 integrated into
    one IC. The MC6802 intruction set is the same as the MC6800.

    The MC6801/3 has increased instructions.

    IF you really want a kicked up 6800, try opencores.org. There is a
    6800 core that will drop into a Spartan 2 FPGA and runs at a E clock
    frequency of 12.5 MHz.

    Today there are a few of the older 8 bit micros that have FPGA open
    source cores that can run at higher speeds than the originals. There
    is even a Z80 core that runs at 35Mhz.

    james
     
  15. Tam/WB2TT

    Tam/WB2TT Guest

    You might want to check out one of the 6805 variants. They may still be in
    production. BTW, if you want to do it on the cheap, use a ~3.58MHz color
    burst crystal.

    Tam
     
  16. "> >>> Freescale suggests Rochester Electronics as a possible source, and
    It's just for fun - I've got a few of them, and I always wanted to make a
    small system out of a 6800 family processor, ever since they were new. The
    6802 means I can use the on board memory for the stack and not have any
    RAM - makes the minimalist retro system one chip smaller...when I get this
    one going, I'm gonna do a Z80 and maybe a TI 9900 - I've got plenty of chips
    from that era due to diligent scavenging, and now I've got a little free
    time to experiment...it's just for, you know...kicks...

    Thanks all for the answer - I'm soldering in a 4 MHz can oscillator
    tonight...the LEDs will be blinking soon...

    Lee K. Gleason N5ZMR
    Control-G Consultants
     
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