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Thread: Sampling at an odd frequency?

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    Default Sampling at an odd frequency?

    I have a project I'd like to start working on. I have an old Macintosh Plus with a bad analog board.

    The oscillator on the original Macs (128K, 512K and Plus) is 15.6672 MHz and is is divided in half for the processor. The video signal on the motherboard is clocked at the full 15.6672 MHz. What I want to do is read that signal with a Prop and output a VGA signal. My concern is that I'm not going to be able to sample that frequency accurately. It would be easier if it were 16 MHz, but Apple has never been known to make their hardware easy to access. The video signal is a 5v TTL pulse, with a low representing a white pixel and a high representing a black pixel.

    Will this be possible with the Prop? One option I'm considering is swapping the oscillator with a 16 MHz version, but I cannot find information on exactly why Apple chose such an odd frequency in the first place and I'm not sure what, if anything, the increase in frequency will do.

    My reasons for doing this project are basically sentimental, but it should also be fun.
    Last edited by ForumTools; 10-03-2010 at 01:52 AM. Reason: Forum Migration

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