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Thread: need Commodore Plus/4 cpu's

  1. #1
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    Default need Commodore Plus/4 cpu's

    I've been given a few, and was told the cpu's crapped the bed. Someone e-mailed me from cctech and said that 6510's should work in place of 7501's. Anyone know?

  2. #2
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    I doubt it. Maybe a heavily modified 6510. The 7501 (8501) was based on the 6510, but has some extra pins to the onboard I/O port for memory banking. It also has an AEC input which gates with the R/W signal from the TED chip (which makes it switch from 1.76 to 0.88 MHz, IIUC).

    It has been reported that the AEC line can be shut off and the computer will run (over-clocked?) anyway. I suppose the 6510 also could handle 1.76 MHz without problems, but if it had been a drop-in replacement, it would be common knowledge among Commodore hackers since many years ago. Try it if you want, but it is likely that you will break both the CPU and the computer (if the other components are not broken yet).

    Having that said, there have been discussion on building a 7501/8501 replacement board consisting of a 6502, a 6522/6526 and some more stuff. It kind of works, but there were problems in operating a tape or disk drive with this replacement board. Web page in Italian.

    http://www.webalice.it/gratteri/65028501.html
    Anders Carlsson

  3. #3
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    I doubt I'll persue it to any degree, but the cpu's of most puters are clocked with an external crystal, so wouldn't changing it to a suitable frequency alleviate any concerns there? I haven't even cracked one of these things yet.
    Are you aware of this site- http://www.ide64.org

  4. #4
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    I don't know which revsions of 6510 chips you have handy, but the 6502 and possibly also the 6510 mod were available in different versions to accomodate 1, 2, 4 MHz. There are some hacks to overclock your C64 to 2 MHz, but I don't know if it damages the processor. Somehow I think changing any crystal or clock generator in the Plus/4 to one that outputs about 1 MHz (like the C64) would work even less than making the CPU run overheated on 1.76 MHz, if it was possible at all.

    Since I don't have the electronical skills to evaluate the board project, I didn't check if Ruud and Daniele are using a 2 MHz version of 6502 to achieve what appears to be 1.76 MHz in the end. I could ask if there was any further progress since the last message on the cbm-hackers list three years ago, but I suppose finding a 7501 or 8501 chip may be "easier" (for a homebrewn-manufacture value of "easy") than building this board.

    If you have a few Plus/4's, is it the CPU that is broken in each one? Otherwise I've read that the TED chip is prone to failure too, so maybe you would find yourself lucky by shifting parts. But you need a way to troubleshoot the computer to identify which part is broken..
    Anders Carlsson

  5. #5

    Default interested in a commodore plus/4 with manuals & guide?

    hi! are you interested in a commodore plus/4 with 2 user's manuals and 1 integrated software manual complete with electrical cord and adapters in original box only wear and tear is on the box itself i have pics if interested.previous owner was a computer repairman.it works as well.all in good condition no kind of damage i can see i recieved it 2 days ago from a friend of mine and he doesnt take electronics that do not work. so if interested let me know.

  6. #6

    Default PLUS/4 's need 8501R1 chips

    Hey Chris...it's fellow MARCHer Bill...I am 99.999% sure that the 8501R1 is the chip you'll need. I have swapped working versions of these chips into all of the plus/4's in your possession and all but one came to life. These chips are found in C-16's and C116's as well. If you find a C16 you can yank that chip and place into the more useful plus/4. I have some plus/4 programs on vintagecomputer.net once you find a chip.

  7. #7

    Default 8501R1 chip available

    Hi there, I've got a brand new chip for sale on Ebay at the moment. You can find the auction at http://cgi.ebay.co.uk/ws/eBayISAPI.d...3713&rd=1&rd=1

    I may be able to get hold of some more...

    Adam

  8. #8

    Default

    It might be useful to note that this thread has been dormant for almost 2 years.
    Or not.

    "It's a me-too, 8-bit machine with good graphics and a disk system nobody will support."
    -- Bill Gates, about the Sony SMC-70 with the new 3.5" floppy drives (InfoWorld; June 7, 1982)

  9. #9
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    Details, details, details!

    Cheers,

    80sFreak

  10. #10
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    Well, if those CPUs are hard to come by, there is a chance that someone has a broken computer since a few years ago, waiting for a matching CPU. Since the OP has left the forum, it is not likely that he will see the eBay link though.
    Anders Carlsson

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