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Thread: C64C JiffyDOS ROM Installation and Adapter Build

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    cjcliffe's Avatar
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    Lightbulb C64C JiffyDOS ROM Installation and Adapter Build

    One of my project goals this weekend was to install a JiffyDOS ROM in a C64C; both of which were obtained from World of Commodore in Toronto a couple years back but had been shelved when I found the C64C's ROMs weren't socketed and I didn't have the appropriate tools or enough practice to remove them.

    I assumed it was going to just require extracting the ROM chip and replacing with a socket, but after taking the shield off I realized my C64C has the 24-pin Kernal ROM, so the 28-pin JiffyDOS ROM I had wasn't going to fit:

    Click image for larger version. 

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    For an added level of difficulty there was also a set of soldered tabs all around the outside that would have to be desoldered as well:

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    Instead of shelving it again and ordering parts, I dug around in my junk boards and found a couple network cards with ROM sockets I could salvage to help build an adapter:

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    The salvaged socket pins weren't long enough to perform the socket-on-socket hacks I've seen, so I decided to try using some prototype boards and pushing pin headers all the way through. My first few attempts failed; trying to put it off to the side required too much wiring (and interfered with nearby components / shield) and the next one I simply messed up the pin header alignment Additionally trying to use a proto board without bus traces made it far too easy to rip off the little circular pads when putting any stress on the pin headers:

    Click image for larger version. 

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    Finally after re-measuring and test fitting everything before assembling (plus using a more robust board with bus traces) the third attempt worked out much better:

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    ( based on the multi-kernal addapter schematics from http://symlink.dk/nostalgia/c64/rom/ )


    With the adapter ready to go all that was left to do was remove the lower shield and extract the Kernal ROM so I could replace it with a socket.

    C64C board with Kernal ROM extracted:

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    Socket installed in place of the Kernal ROM -- Didn't have any 24-pin sockets, so I just clipped 4 pins from the bottom of one of the salvaged 28-pin sockets:

    Click image for larger version. 

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    And after all that I was finally able to try the ROM and was happily greeted with the JiffyDOS branded startup screen

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    A1000 0.5M; A500 1M; A500+ 1.5M A500+/030 33Mhz 10.5M, MMR, IDE68k, 500RX, HxC Internal, Indy ECS & 4G CF
    A600/030 25Mhz 34M, ACA630, A604, Indy ECS & 8G CF A1200/030 42Mhz 66M, ACA1231 & 8G CF
    A4000D/040 33Mhz 18M, DVD, X-Surf & 8G CF C64; C128 +uIEC/SD Internal & JiffyDOS

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    Default Finishing up the build and programming my own JiffyDOS ROM

    After I'd gone to the effort to build an adapter that included bank switching support I figured I might give the old-school EPROM burner I was given a try and roll my own JiffyDOS ROM. I loaded up the EMP10 and prepared a JiffyDOS+Original Kernal image by merging the ROM files into a single 32k such that one image appears in the high bank and one in the low bank:

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    To accommodate the bank change all that was needed was a switch to pull-down address pin 27 to pin 14 (ground) on the chip itself; optionally it seems I could have done 3 images by adding a two position switch and connecting the second position to pull-down address pin 26 instead.
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    A quick test showed the ROM was working; I could boot, then turn off and change ROMs via the switch just the same as the JiffyDOS ROM-El version:
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    Putting it all back together required the shield to be replaced (It includes the keyboard supports in this model) so I made some cuts with my trusty Radio Shack Nibbler and then installed the switch:
    Click image for larger version. 

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    And finally everything is back together and working well I might see if it's possible to do some indoor retro-bright and order a new badge for it -- I also have a uIEC/SD for it that could be installed internally some day.
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    Last edited by cjcliffe; 12th February 2018 at 06:21.
    A1000 0.5M; A500 1M; A500+ 1.5M A500+/030 33Mhz 10.5M, MMR, IDE68k, 500RX, HxC Internal, Indy ECS & 4G CF
    A600/030 25Mhz 34M, ACA630, A604, Indy ECS & 8G CF A1200/030 42Mhz 66M, ACA1231 & 8G CF
    A4000D/040 33Mhz 18M, DVD, X-Surf & 8G CF C64; C128 +uIEC/SD Internal & JiffyDOS

  3. #3
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    Excellent Solution but please read on....

    Your current solution means that when you ground pin 27 to access the other image you are shorting the Hi Signal on 27 to ground.. This is not good practice and something will give at some point...

    Try this 'Safe method'

    Use pliers to straighten pin27 so that it does not make contact with the socket then use a small 4k7 resistor between Pin 28 and Pin27, your existing wiring is spot on.
    This will isolate your Hi/Lo switching from the C64's Address Bus line ensuring you are not stressing anything.
    This is actually how the Official JiffyDOS ROM is wired up too.

    Regards
    Bas
    Ritchie Blackmore's Rainbow June 2016, I Was There

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    cjcliffe's Avatar
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    Question Multi-Kernal Schematic

    Quote Originally Posted by TheCorfiot View Post
    Your current solution means that when you ground pin 27 to access the other image you are shorting the Hi Signal on 27 to ground.. This is not good practice and something will give at some point...
    I think I understand what you're recommending, and it makes sense for a C64 with 28 pin ROM; but unless I've missed something, based on the schematic I used from http://symlink.dk/nostalgia/c64/rom/

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    Pin 27 on the adapter isn't actually connected through to the C64's 24 pin socket; the only thing it's connected to is Vcc/Vpp through a 2k2 resistor which gets pulled down to ground when the switch is enabled.
    A1000 0.5M; A500 1M; A500+ 1.5M A500+/030 33Mhz 10.5M, MMR, IDE68k, 500RX, HxC Internal, Indy ECS & 4G CF
    A600/030 25Mhz 34M, ACA630, A604, Indy ECS & 8G CF A1200/030 42Mhz 66M, ACA1231 & 8G CF
    A4000D/040 33Mhz 18M, DVD, X-Surf & 8G CF C64; C128 +uIEC/SD Internal & JiffyDOS

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    Perfect the 2k2 resistor is doing exactly the same job, For some reason I kept thinking C64C lol
    Ritchie Blackmore's Rainbow June 2016, I Was There

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