So what can be more cool than this internal 512KB expansion is a 1MB or 2MB internal expansion ...

Hehe, more is always better! I could certainly do a 1mb or 2mb expansion using multiple 512kb SRAM chips and expand the GAL to provide the correct chip enable for each SRAM.

Or you could modify the existing SRAM board by soldering the SRAM directly to the board without a socket (to give extra clearance) and piggy back another SRAM on the top. With a modified GAL you could use another output to provide the chip select for the 2nd SRAM with a piece of wire between the GAL leg and the SRAM chip select leg.

I might give this a go if there is any interest? 512KB is enough for me, but I could possibly provide a 1mb board for £20... I'd just need to make sure there is enough clearance in the case.

Or you could modify the existing SRAM board by soldering the SRAM directly to the board without a socket (to give extra clearance) and piggy back another SRAM on the top. With a modified GAL you could use another output to provide the chip select for the 2nd SRAM with a piece of wire between the GAL leg and the SRAM chip select leg.

Good idea!

Can I ask where (and how) you order those GALs (and maybe the SRAM) exactly? Or is it some kind of "secret source"?

I just search eBay for components from international sellers. For GAL's I found these - http://www.ebay.co.uk/itm/10PCS-IC-GAL16V8D-GAL16V8D-25LP-DIP-20-NEW-GOOD-QYALITY-tracking-number-/300920600072?pt=LH_DefaultDomain_0&hash=item461043f608

I've had no problems ordering from overseas sellers so far, other than it can sometimes take a long time to arrive!!

I have also been trying surface mount components, but soldering with a soldering iron is very hard for SMD. So I have bought myself a hot air rework station, but it need some practice with solder paste...

Update: Current orders from Hungary: 10!

all the Hungarian orders will go out together when I get the next batch of PCB's.

The 1M version can be chosen? It is a +5 GBP?
I will ask which version wanted.

Yes, if you would like to find out how many 1MB / 512KB versions people would like, I will try and got those built. I've checked the clearance, and it looks ok to me, so the only thing left to do is to program a different GAL and hook up a bit of wire for the 2nd chip select. And, yes, I can do the 1MB for £20.

My only concern is heat in the bottom SRAM chip as it will have no ventilation with the 2nd SRAM on top of it. The chip will run up to 85 degrees centigrade according to the datasheet, though, so I don't think it should be a problem. The SRAM was only slightly warm in testing.

I have no idea about the temperature and the datasheet in this case, but maybe - in general - the "worst" temperature is at the boundary of working conditions ie, very rapid r/w access near the max speed of the memory, as the needed curren to supply on Vcc is related to the frequency in general (and temperature is related the current after tall, emitted heat because of the resistance, etc). So if your SRAM is 70ns I doubt it will be near to 85 degrees if the memory accesses in general occurs more rarely than 70ns ... Well, at least if that number of 85 is defined for the maximum temperature at the most "extreme" usage given by the specification.

I have no idea about the temperature and the datasheet in this case, but maybe - in general - the "worst" temperature is at the boundary of working conditions ie, very rapid r/w access near the max speed of the memory, as the needed curren to supply on Vcc is related to the frequency in general (and temperature is related the current after tall, emitted heat because of the resistance, etc). So if your SRAM is 70ns I doubt it will be near to 85 degrees if the memory accesses in general occurs more rarely than 70ns ... Well, at least if that number of 85 is defined for the maximum temperature at the most "extreme" usage given by the specification.

Yes, I agree. The SRAM is actually 55ns, so it is running way below it's maximum frequency, and will be drawing more current while switching. So it should be running cool compared to what it can do.

Zozo: Wow, that chip stack is awesome!