Re: Dead PET 2001 with 6550Žer

From: Nicolas Welte (
Date: 2002-04-16 14:08:00

  • Next message: Nicolas Welte: "Re: Dead PET 2001 with 6550Žer" wrote:
    > FYI, I face the same problem. But I have the advantage of a second working
    > PET :)
    The same here :-)
    I'm going to make a replacement RAM/ROM card that plugs into the 6502 socket
    of the original PET, and then all the ROMs and RAMs can be put in a safe
    place. As a nice side effect, it will offer the full 32kB RAM, maybe
    switchable to 4k, 8k and 16k configurations, as well as switchable ROM
    versions. This shouldn't need more than a 32kB SRAM chip and a 32kB EPROM
    chip plus some glue logic. Is there any use for an option ROM socket for a
    combined 16 or 32kB option EPROM? When I have the PCB layout ready and
    tested, it will be uploaded somewhere, of course.
    One problem that remains is the video circuit, it also uses a ROM and two
    RAMs that are not replaced by this board. I got a schematic (reverse
    engineered by Paul Förster) of a very simple 6550 replacement board that uses
    only one 2114 and one 4000 series gate chip (combined NAND, OR, NOR) that
    could be used to replace the video RAM, and for the character ROM, either
    make an adaptor socket for a 2716 or bigger, or hope it will last for a
    This should keep our PETs running safely for this decade or longer :-)
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