Re: [stella] Pokey Mod For A 2600

Subject: Re: [stella] Pokey Mod For A 2600
From: emooney@xxxxxxxxxxxxxxxx (Erik Mooney)
Date: Sat, 18 Oct 1997 20:40:02 GMT
>>Or if there's a way to duplicate the effects of this custom activision 
>>chip internally.
>>Writing to the TIA sound on each scanline would give you what?
>>192 x 60Hz... 11.52KHz sample rate... not too bad for a 2600.

Not quite.  A line is 76 cycles... at 1.19 MHz, a line is 1/15263 of a
second, for a sample rate of 15263 Hz.  Your mistake came because the 60 Hz
frame is actually 262 lines... that * 60 Hz = 15720.

Why the difference between 15263 and 15720, though?  The docs give the NTSC
graphics clock as 3.5795 MHz.. if the CPU speed is 1/3 of that, which is
1.1931667 MHz, the actual lines-per-second sample rate would be 15699.6 Hz,
which is close to but not exactly 15720.

These subtle timing differences might add up and be causing your clock to
gain or lose time on the order of a few seconds a day, if you're tying your
clock indirectly to a 1.19 MHz clock when it's actually 1.19317 MHz.

Hmm, now we know why 2600s were never used for military applications :)

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