BIOS Swap?

[dan9550]

Hi, i have a few PSXes sitting around, i was curious if it is possible to say take the BIOS from a SCPH-9002 and use it in a SCPH-5502?

That way i could in theory use the nicer (and more nostalgic) bios menu that also has the cd audio visualizations on the psx with the parallel port.

Anyway im starting to make no sense explanations as to why it will / will not work appreciated

[nocash]

I don't know of any compatibility issues, except one small detail: Port 1F801060h is initialized differently in older BIOSes (probably related to different DRAM chips installed on the mainboard), but you could patch the corresponding bytes.
If you are planning to install a socketed rom/eprom then you might notice that the PSX case isn't as big as it looks like (particulary there isn't much space between mainboard and cdrom drive).

[DD-Indeed]

But is like a first rule, that bios is always desinged to specific kind of motherboard and therefore cannot be installed on a different one ?

[Administrator]

No, you can mix and match them.

[dan9550]

So in "theory" if i was to desolder the 9002 bios and threw it in the 5502 it would work fine?

[Administrator]

Correct. My only doubt is what no$cash said, so the later PSX models and the PSone may have problems, but give it a shot. It won't fry anything.

[dan9550]

I may get around to it, really would like the newer BIOS on the PS1 that has the parallel port (which i plan to use for PSIO when that arrives). In the mean time i got a whole laser mech for $8 from china

Would someone be so kind as to point me in the direction of the BIOS chips? I have a suspicion as what ones they are but not 100% sure.

[dan9550]

Ahh i did some google-ing found it on the 9002 (PU-23) board as IC102 it has sony written on it, i should be able to remove that with some patience. Would anyone who has a bit more electronic know how be able to tell me if its possible to do something similar to this.

http://i36.photobucket.com/albums/e36/D ... dc_va1.png

So like have the newer bios chip soldered on top of the existing one and have a way to toggle between them?

[Administrator]

You should be able to do that. I remember thinking about doing something like this too.
I know that Skywalker of the HITMEN made one here using SRAM.
Whether it worked or not, I don't know because I find it amazing that there is no interference or crosstalk

[dan9550]

Well looking over it again, the CE pin is the only one i'll need to touch really. It gets 3.3V but also connects to something else right? or does it just connect straight to the CPU?

If thats the case and it connects to the CPU i can just make a switch which changes which chips CE is connected to the CPU to select the BIOS?

[Administrator]

Yes, it goes directly to the CPU but first thought a 100R resistor.
Yes, you can switch it, but don't do it whilst the CPU is running

[dan9550]

Thought so, should be pretty simple then hard part will be soldering it. So your tempting me now what exactly happens if i switch it when the CPU is on xD i know it will be bad but what!?

[Administrator]

The PlayStation will crash.

[dan9550]

aww no magic smoke

[Administrator]

Hmm... if you switch /CE whilst the PSX is in the bathtub with you then maybe you will get magic smoke and a new hairdo

[dan9550]

So i got it all installed and... wait for it... Yeah nothing lol

I did accidentally lift pad 28 under the original bios :\ so i suspect my "fix" for that is the cause

Will keep investigating!

[dan9550]

So i've checked that pin 28 connects to pin 140 on the CPU, so i've fixed that. Even when i have the CE pin for the original BIOS connected i still get nothing. So im out of ideas here, would anyone be able to help please?

[Administrator]

Photos?

[dan9550]

Here you go:


Not the prettiest job, used some cut up resistor legs to join a few of the pins. Not so bad that it shouldn't work IMO anyway

[Administrator]