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Thread: A useful 68000 deveopment machine

  1. #1

    Default A useful 68000 deveopment machine

    I was looking at the earlier post on the development system with key pad and LED display. Although, these machines are fun to fiddle with and clearly collectable. If I were doing anything serious with a 68000 I'd want an assembler and disk drive.
    When I look at this, I realize that I already have such a machine. The Canon Cat could meet these requirements. I've even rigged mine up to recompile its own firmware.
    A small amount of Forth code could input and output in HEX or Motorola format. Some of this code is already written and just needs to be adapted.
    One thing to know, there is a design flaw in the disk drive. There is a simple fix. If you think it is working fine I can assure you it will fail and when it does, you'll end up ripping the head assembly off, making the drive unrepairable. Since it is a special drive, it is hard to find a replacement. It would take a 740K drive with DriveReady signal and rewiring.
    If anyone reading this has a Canon Cat, that hasn't had the drive repaired, contact me or Jack Rubin. We can help you fix the problem before you destroy your drive!
    Dwight

  2. #2

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    What 68000 software do you want to develop?

    By coincidence, a few days ago a person contacted me about my T68KRC ( https://www.retrobrewcomputers.org/d...z:lasmo:t68krc ) clear out of the blue. I have not done anything with it for about a year other than porting CP/M-68K to it. I wasn't sure I even know how to build more. So the last few days I built up 3 T68KRC and they all worked (i.e., pass memory diagnostic and boot up CP/M68K). Now I want to improve the documentation and develop more software for it.

    What 68000 development tools are you using?

    Bill

  3. Default

    Sierra C/68k on DosBox here

  4. #4
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    Default

    Quote Originally Posted by Dwight Elvey View Post
    One thing to know, there is a design flaw in the disk drive. There is a simple fix. If you think it is working fine I can assure you it will fail and when it does, you'll end up ripping the head assembly off, making the drive unrepairable. Since it is a special drive, it is hard to find a replacement. It would take a 740K drive with DriveReady signal and rewiring.
    If anyone reading this has a Canon Cat, that hasn't had the drive repaired, contact me or Jack Rubin. We can help you fix the problem before you destroy your drive!
    Dwight
    can you just describe the fix here?

  5. #5

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    It is kinda surprising to me how relatively under-represented the 68k is in the homebrew community compared to, say, the 6502 or Z80. I suppose that's just down to the relative complexity of designing for a 16-bit bus compare to an 8-bit one.

    This reminds me, I should really see if I can find a solution for emulating HP-IB storage devices so's I can try getting something running on my HP 9000/360...
    Computers: Amiga 1200, DEC VAXStation 4000/60, DEC MicroPDP-11/73
    Synthesizers: Roland JX-10/SH-09/MT-32/D-50, Yamaha DX7-II/V50/TX7/TG33/FB-01, Korg MS-20 Mini/ARP Odyssey/DW-8000/X5DR, Ensoniq SQ-80, E-mu Proteus/2, Moog Satellite, Oberheim SEM
    "'Legacy code' often differs from its suggested alternative by actually working and scaling." - Bjarne Stroustrup

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    I don't think it's the 8-vs-16 bit thing--otherwise, you'd see lots of homebrew using the 68008. I think it's three things--the outsized DIP package and the real lack of supporting and easily-interface peripheral chips--and the availability of easily-adapted software.

    Let's face it--when you get a x80 CP/M system going, you have lots of possibilities for software.

  7. #7

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    I suppose that's true - outside of various Forths, most 68k software tends to be highly platform-specific and geared towards one of a couple specific commercial OSes.
    Computers: Amiga 1200, DEC VAXStation 4000/60, DEC MicroPDP-11/73
    Synthesizers: Roland JX-10/SH-09/MT-32/D-50, Yamaha DX7-II/V50/TX7/TG33/FB-01, Korg MS-20 Mini/ARP Odyssey/DW-8000/X5DR, Ensoniq SQ-80, E-mu Proteus/2, Moog Satellite, Oberheim SEM
    "'Legacy code' often differs from its suggested alternative by actually working and scaling." - Bjarne Stroustrup

  8. #8
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    I seem to recall that when the 68K was announced, visions of Unix danced in a lot of designers' heads. The basic features that were needed were there, so a 'port was not terribly complicated. But Unix does require a fair amount of memory.

  9. #9

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    I'm active in the retro homebrew computers circle. There are many people wanting to design/build 68000 homebrews, but few are actually being built. Whereas new Z80 homebrews are popping up just about every month. 68000 & peripherals were very expensive in its day, but nowadays it is just a few dollars more in the grey market. I've built both Z80 and 68000 homebrews and I know one of the difficulties with 68000 is the minimal system needs two EPROM and two RAM that won't fit in the cheap 100mm X 100mm pc board. Furthermore, there are not as many 68000 & CP/M-68K expertise out there compare to Z80. CP/M-68K is cool that its TPA can be as large as 16 meg without complicated banking scheme, so quite a bit of sophistication can be incorporated in the BIOS without worrying about using up the precious memory space. 68000 assembly code is also a real pleasure to write. With help of CPLD, I did managed to put 68000 homebrews on 2-layer 100mm X 100mm pc board, so cost wise, it is not much more than Z80 homebrews. The biggest drawback of 68000 is there are very few CP/M-68K software available.
    BillTiny68K.jpgT68KRC.jpg

  10. #10

    Default

    Quote Originally Posted by Al Kossow View Post
    can you just describe the fix here?
    The problem is the guide rail is held on with a small piece of nylon at both ends. The front end doesn't seem to have an issue but the back piece is over stressed and 100 percent of the drives I've seen, the piece is cracked. When is lets loose, the head will not retract all the way and catch on the metal cover of the floppy when being ejected. The piece is held on with both a screw and a nylon rivet. On my drive, I made a new piece of of a different plastic material and held it on with the screw, not under high tension. Jack just used some WD weld to glue it down. The only issue I see is to avoid blocking the full travel of the head guide.
    To open, I recommend not removing the bottom PC board but rather, remove the top cover first. Use care on the keyboard connector. The IDC connector from the floppy cable is stuck on real hard so be careful to get it off the mother board. Remove the drive with the bracket before removing the drive from the bracket. Open the drive and then remove the piece that lowers the head and you'll see the rail.
    The reason the heads get ripped off is that most will accidentally pull too hard on the drive. Pop goes the head.
    If you have any issue, I can stop by and show you what to do.
    Dwight
    Last edited by Dwight Elvey; June 22nd, 2019 at 10:43 PM.

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