3 ms·

The 6502's two-phase clock throws a wrench in direct clock speed comparisons, no?

• edmccard 10y ago
  >The 6502's two-phase clock throws a wrench in direct clock speed comparisons, no? Not really? The two phases are more or less just inverted versions of each other[1], but 1 clock cycle, for the purposes of counting cycles-per-instruction, is the same time (I think) whether you're measuring phase-1-high to phase-1-high or phase-2-low to phase-2-low. [1]http://lateblt.livejournal.com/88105.html http://lateblt.livejournal.com/88105.html
• avhon1 10y ago
  The "two-phase clock" is just the alternate halves of one square wave. The 6502 accesses memory during one half and processes during the other. Only one clock signla is needed, and one instruction will be completed at the end of every complete clock cycle.
  • david-given 10y ago
    Fun fact: you can run a dual core 6502 system by hooking up the two processors to the same memory bus, one using an inverted clock. (Slightly more complicated than that, but only slightly.) The Commodore Pet disk drives used this trick; one processor was the application processor, which listened for IEEE488 commands and handled the disk format; the other processor handled the low-level stuff (we'd call it a DSP today). Yes, the Pet disk drive did have twice the number of processors as the computer it was attached to. http://www.6502.org/users/andre/petindex/drives/arch/index.html http://www.6502.org/users/andre/petindex/drives/arch/index.h...
    • digi_owl 10y ago
      And then you got the Amiga that apparently took that a step further by having the chipset act independently of the cpu, with a but of circuitry sitting in the middle to make sure they didn't both access the shared ram at the same time.
• moonbug 10y ago
  It's immensely charming that you are keeping lit the flame of this three decade old argument.