Saturn main clock frequency

Discussion in 'Sega Saturn Programming and Development' started by hitomi2500, Jun 1, 2015.

  1. hitomi2500

    hitomi2500 Site Supporter 2015

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    (Un)official schematics, wikipedia, and multiple other sources give a 28.6 MHz frequency for SH-2 CPUs. But when i measure MCLK2 (which is the same as MCLK3, which goes directly to both processors) with a scope, it gives me 26.88 clock in bios at time/date entry screen. Haven't checked this in games yet. The question is, is it possible to change the main clock via software? Or is my scope mistaken?
    I want to multiply this clock for my own purporces, but if it's changeable, there might be undesired side effects...

    Nevermind, i've alredy found the answer in the sega's docs. The freq differs indeed, but it depends on videomode (NTSC/PAL) and video lines number (320/352) only. Actually it's kind of a strange thing to do such a dependency, saturn was never built with too much economy in mind... Maybe syncing cpu with VDPs was a problem?
    Well, i'll have to use SCSP clock instead, that one seems to be steady 22.5792MHz.
     
    Last edited: Jun 1, 2015
  2. Druidic teacher

    Druidic teacher Officer at Arms

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