Overclock PlayStation 1

[Ocelot85]

So I'm wanting tooverclock my PlayStation 1 a little higher than the stock speed.
I know that I need to connect the new frequency to Pin 4 on the CPU  but I'm not sure what I'm supposed to do with a the new crystal.
Obviously one terminal comming from the crystal connects to the CPU but what does the other terminal do?

[kendrick]

Go to ground? This is just a guess, but I'm thinking that a lot of functions (like video sync and controller timing) are tied to that crystal, and not just processor speed. You may not get the result you're looking for.

[Ocelot85]

From what I can see, the GPU get its frequency from a different pin on the clock chip than the CPU.
So clocking to CPU higher shouldn't interfere with the video.

According to this site: http://www.telecable.es/personales/ccs/inforepar.htm
On the clock chip (IC204)
Pin 1 = 53.203 MHz  (GPU)
Pin 5 = 67.737 MHz  (CPU)

So clocking to CPU higher shouldn't interfere with the video.

PlayStation 1's seem to half whatever the frequency is coming in.

53.203 MHz =26.6015 MHz (GPU)
67.737 MHz = 33.8685 MHz (CPU)


So to get the CPU running at 40 MHz I need an 80 MHz crystal, I just need to obtain one and then be sure on how to install it.

[Ocelot85]

RobIvy64 had a guide for overclocking a PS1 on his site a few years ago, but it is no longer available for me to reference and I'm not positive on how to connect the crystal oscillator. I've also had no luck obtaining an oscillator at that high a frequency.

[Ocelot85]

I came across this PDF a few days ago and I believe that it's for the PS1 clock generator.

Inside it says "Outputs ranging from 500 kHz to 100 MHz (5V) and up
to 80 MHz for 3.3V operation"

I'm wondering if it's possible to change the frequency it outputs by changing the voltage going in to it, but I'm no expert so I'll ask you guys.

This may be easier for me as I can't find a store that sells oscillators higher than 20 MHz.

[l_oliveira]

Clocks for the SPU (sound processor) and CD-ROM drive are derived from the CPU. They run at 33mhz (which is half of the 66mhz crystal connected to the CPU).
Overclocking will have adverse effect on sound (higher pitch on the sounds and music. Speed/rhythm is likely set by the video interruption so that will be not affected)
Might have adverse effect on the CD-ROM drive (surely will cause it to run faster than it's spec) which may result on read errors in discs.

I say go for it, but make sure you leave a way to "undo" it should you need.

[Ashen]

I've runned PlayStation CPU on almost 100MHz clock (it means CPU runs on 50MHz). But - picture is broken (since CPU have mismatch sync with GPU) and sound is too fast. On modded console i've unable to run any game CD. Only AudioCD runs. May be it because mod-chip, but i didn't disconnected it yet ^_^ After some jumping around i've did cut out clock generator from old PC motherboard. And this was my regulated clock source (it can change it's clock by jumpers, not via data bus.). Clock to SPU i've manage from original 67.737MHz oscillator but through simpliest divider of clock with /2 ratio... So there is a place for experiments yet. At least i know that some arcade board based on PSOne hardware have CPU runned on 100MHz (with 50MHz on CPU core).

[l_oliveira]

These are based on a different PS1 CPU.  Games that run on Namco's System 11 use the old PS1 CPU (100x series)
Games running on System 12 (like Tekken 3 and Tekken TAG) run with that new 50mhz CPU.

[Ashen]

That's right ^_^ But there is not only another CPU... I think that timings (reply frpm GPU, SPU, CD-ROM etc...) in BIOS also different. And System 12 boards don't used PSX SPU - there is another sound subsystem installed.
But i think that is possible to add some RAM (up to 8Mbyte in bank 0 and another 8Mbyte in bank 1) and Video RAM (just soldering one more SGRAM chip to GPU.)
But what is more important is there is a chance to reverse engineering CD-ROM drive, make IDE interface with some microcontroller and use external HDD for loading images.
But it takes a lot of time and need advanced programming capabilities.

[Ocelot85]

Shouldn't a HDD be possible over the parallel port, or would that require a custom BIOS?

[Tiido Priimägi]

nobody will stop you from interfacting a HDD to some system, but nothing will make use of it unless something is written to make use of it... I don't know how PSX handles data, but a custom BIOS can possibly enable use of HDD for every game there is

[Ashen]

That's right. But there should be also some kind of resident module, which allow to switch images on multidisc games. Also there is a possibility to make saving onto HDD directly. But everything will require huge BIOS rewrite.
By the way, do not forget that is possible to build a CD-ROM drive interface, on one end of it will be PSX interface, on other - normal HDD's IDE.  And as soon there is pirated games with possibility tu run disc with multiple games on it, it can be rewritten to do so from HDD directory. But who will do such thing? I can spend my time to hardware develoment, but without software it still be a pile of junk.