SmaCK - Small(est) ClocK replacement for MOS8701

Create (yet another) MOS/CSG8701 replacement for the Commodore64!

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Over the last few years quite a few 8701 replacements were made with readily available components but they all were quite large compared to the original MOS8701 chip (DIL16). I was aiming for a replacement with a similar size as the original chip and finally found the time to do that while testing my new vapor phase reflow oven...

Another nice feature which no other 8701 replacement implements so far:

Automatic selection of PAL/NTSC frequency

depending on the board settings. So this is the first real drop-in replacement!
Of course the frequency can also be fixed to PAL OR NTSC frequency via
solder bridge on the bottom.


Preliminary(?) schematic for the soon to be published full project.

Adobe Portable Document Format - 58.04 kB - 12/20/2019 at 08:22


  • Mass produced SmaCK available...

    androSID01/07/2021 at 12:09 0 comments

    I already started mass production some time ago and they are readily available! Just in case...

  • Preparing mass production now!

    androSID02/26/2020 at 08:08 0 comments

    No real news; I'm just currently preparing production files for a small run of this little hardware.

  • A question about the optical appearance

    androSID12/20/2019 at 08:49 0 comments

    I was asked if it wouldn't have been better (means: nicer) to turn the chip
    on my replacement by 90 degrees?

    Well I actually wanted to do that (because I'm also trying to do visually appealing replacements). Unfortunately the bottom side of SmaCK (sic!) is quite full already! But see yourself:

    I would have had to move parts from the top to the bottom layer and (even worse) would have more vias in the signal path which would degrade the two generated clocks... something I really didn't want.

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Enjoy this project?



n13ldo wrote 04/23/2021 at 08:25 point

Where are the assembled boards available? UK/Euro ?

  Are you sure? yes | no

androSID wrote 04/23/2021 at 08:35 point

I sold most of my stock to a shop:

In case the german language is a problem just drop me a line... I still have enough assembled boards available.

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tyristori wrote 11/15/2020 at 13:42 point

What component is U2?

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androSID wrote 01/07/2021 at 12:10 point

Clock generator for PAL+NTSC

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Starhawk wrote 12/20/2019 at 19:23 point

OK, dude, you done taught me a thing. Or at least half of it... school me: what is the 8701 and what does it do?

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androSID wrote 12/20/2019 at 22:55 point

The 8701 is a PLL used in a later version of the Commodore 64 to create the dot clock and color carrier needed for the video chip.

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Starhawk wrote 12/21/2019 at 02:05 point

Do I remember correctly that the 556 is what does that (along with a few other chips, I... think?) in the earlier machines...?

  Are you sure? yes | no

androSID wrote 12/21/2019 at 09:16 point

No. 555/556  are timers - not clocks.

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