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Anyone Increased 5500/6500 VRAM to 4 MB?

trag

Well-known member
I was admiring my new 5500 board yesterday and noticed the NEC PQFP VRAM chips. They look just like the Samsung KM4132G512 chips I have on hand. So I checked the Hardware Developer Note for the 5500/6500 and it is indeed SGRAM, which means that it is almost certainly pin compatible (there are JEDEC standards for most memory pinouts). I still need to find the datasheet for the NEC part and compare.

So the question becomes, has anyone tried increasing the VRAM capacity on one of these things to get more color depth or video resolutions? Apparently it all depends on whether Apple connected pin 30 of the VRAM chips to a memory line.

The 100 pin QFPs aren't all that difficult to solder/desolder especially if one does not need to reuse the old ones.

 

trag

Well-known member
Okay, never mind. I examined a 5500/6500 board last night and there are no traces to pin 30 of the VRAM chips, so the needed extra address line is not supported. Darn. I have like 2000 of those chips on hand. It would have been nice to use 2 of them...

On the other hand, the extra address line may be available on the Rage II chip and could be wired into place. But that's more effort than I'm willing to exert at the moment. Anyone have a pinout for the Rage II chip and/or a datasheet?

 

Dennis Nedry

Well-known member
I would use an audible tester to find each existing address connection from VRAM to the graphics chip, and see if a pattern emerges. If so, you have your extra address line!

The next issue is how to tell the graphics chip to look for more VRAM. It may be possible to compare VRAM cards of different capacities from very old G3s and iMacs and see how they differ when they interface with the graphics chip.

 

Trash80toHP_Mini

NIGHT STALKER
I assume you were planning to "Piggy-Back" the chips on top of the existing VRAM? :?:

One "rework" jumper shouldn't be TOO noisy! }:)

Don't most Video Controllers just poll for VRAM configuration at startup?

 

trag

Well-known member
I assume you were planning to "Piggy-Back" the chips on top of the existing VRAM? :?: One "rework" jumper shouldn't be TOO noisy! }:)

Don't most Video Controllers just poll for VRAM configuration at startup?
Nope. I was planning to replace the whole chip. The chips I have are twice the capacity. There are also chips with four times the capacity, but I only have a few of those and yet another pin would have to be implemented.

I have the datasheet for the VRAM chips. What I don't have is a datasheet for the Rage II chip.

 
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