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more notes about timings on psx 

Signed-off-by: Leah Rowe <info@minifree.org>
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Leah Rowe 2024-09-26 12:13:55 +01:00
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site/docs/install/playstation.md
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@ -169,6 +169,30 @@ on PAL consoles (and vice versa); RGB SCART can be used to mitigate the colour
issue, but not the timing issue. The oscillator mod is the only solution for the
timing issue.
The PAL GPU clock is roughly 53.2MHz, and divides by 12 to create the PAL
subcarrier/colorburst signal; this is needed in composite video for example.
The NTSC GPU clock is 53.693175MHz, and divides by 15 to create the NTSC
subcarrier/colorburst signal; ditto, this is used for NTSC composite video.
On a PAL playstation, Sony woride 53.2MHz to both inputs, and on NTSC, wired
53.69MHz to both inputs; that means on NTSC machines, PAL games will run with
a 3.579545MHz colorburst signal, and on PAL consoles running NTSC games,
the colorburst would be 3.55MHz.
On *most* consoles except very early launch/debug models, and *very late* slim
models, the PAL clock is pin 192 on the GPU and NTSC is pin 196 on the GPU.
The Dual Frequency Oscillator mod uses a programmable oscillator and taps into
the video mode signal off of the GPU to know whether PAL/NTSC is used; it
switches the master clock hooked up to both inputs accordingly.
Another method is to *cut* the line going to the NTSC pin on a PAL console,
and wire a 53.69MHz oscillator (at 3.3V, with the output through a 220Ohm
resistor) directly to the pin; on an NTSC console, do the same but cut 192
and hook up 53.2MHz to it. The Dual Frequency Oscillator method is easier and
therefore recommend, but you can do this other method, which I call *DO* (Dual
Oscillator. Because it's two oscillators!)
Modchips
--------