DayStar PowerCard 601 and upgrading the L2 Cache to 1MB?

[hyperneogeo]

So I was looking at the L2 cache card and noticed that it had 32 pads for each chip, but was using only 28 of them for 32x8 (256k).

The original chip on there is: https://www.datasheetarchive.com/pd...516765643adf153033d176e&type=O&term=KM68257BJ x8

Looking at the pads, I see they are all connected (except pin 1 which is NC) and do match for example 128kx8 (1mb) :

https://www.mouser.com/datasheet/2/198/integrated%20silicon%20solution%20inc_61-64c1024al-1169755.pdf

Where as CE2 is suppose to be high (which is the original VCC for the 256k chip, so that's fine). All of the other pins are actually connected to each other and going to the connector.

Seeing how there is no 32 pin 256k chip afaik, maybe they were planning on upgrading the cache later own the road?

I actually tried replacing all of them with the 128kx8 chips an of course got the death gong. So my guess is the GAL at the bottom is controlling it some how? Luckily the gal itself was unlocked, so I dumped it. I have attached the gal. (Btw I'm aware the MC88915TFN133 isn't there, I just took it out)

Any thoughts?

 

[dkjones96]

I am thinking of trying this same upgrade! Ha! Even ordered the same 128Kx8 chips.

My GAL chip isn't socketed but I did notice that there are some R positions underneath the cache board with 0 ohm resistors across them. I'm guessing that the cache chip has to have a jumper setting change to make the GAL know what to do. There aren't a lot of available pins on those GAL so it must handle only address and control lines.

These aren't fast-page or anything like that so it shouldn't matter but it should be noted that the row/column address lines do move around a bit between the 32k and 128k chips.

It's also possible that they built the cache card with the plans to do a 1MB option but never actually implemented it in the GAL.

Do you still have the cache card with 1MB on it or did you revert back to 256k?

 

[croissantking]

Why don't you try experimenting with different options of the 0 ohm resistors and see what happens?

 

[Phipli]

Why don't you try experimenting with different options of the 0 ohm resistors and see what happens?

Because replacing the card would cost a fortune

 

[croissantking]

Because replacing the card would cost a fortune

Op already replaced all the cache chips!

In for a penny, in for a pound.

 

[dkjones96]

That will 100% be the path I take. The new cache chips are in and will be swapped out, possibly end of the month. Gotta see when I get the courage to do it!

I also now have a set of soldering tweezers so swapping the 0-ohm resistors will be a cinch. Last bit of research I need to do is make sure that the address lines do, in fact, lead back to the cache controller. It's unlikely but possible that they don't as this board was never even advertised with a 1MB option.

Best I can tell there are 5 pairs for the resistor settings. That means, at most, 31 different configs to try.

 

[dkjones96]

Tried the chip swap and, surprisingly, didn't even get the death gong?

I also tried every combination of resistors I could on the bottom and got zero out of the machine.

@hyperneogeo you are certain you got a death gong out of it?

 

[hyperneogeo]

yeah, mine death gonged heh