One of the reasons why it is not possible to use just any type of RAM in a 3000 is because of the memory refresh system impersonated by RAMSEY
Ermm, 30 pin and 72 pin SIMMs would run just fime from the Ramsey timing.. ok you couldnt stick SD-Ram in but a 72 pin adaptor would be much easier to do. (And has been done before, including free designs available from Aminet today)
I found this chip on Digikey which can be purchased by the unit for 11$ each: http://download.micron.com/pdf/datasheets/psram/BurstCellularRAM1.5_128Mb.pdf This chip has 16 data lines and contains 128Mb of data therefore two of them fullfills the 32bit data bus requirement for 68030, 040 and 060 processors and give you 32MBytes for 22$. I
Ermm its a 16 bit chip that gives you eight megabyte of memory, sticking two side by side (Connected to the same address pins) would give you 16, an address decoder would be needed for 32. (and four memory chips)
I can't believe you are trying to charge people $22.00 for only 32 MB of ram. That smells outrageously expensive. Well, I wish you real good luck getting the corner PC store's DDR SDRAM to work on a 68k based Amiga...
I think he was commenting on your use of "outrageously expensive" when talking about the ZIP ram, it isnt expensive (Your not ment to use it for adding loads of ram, at 1meg its cheap) its just there are cheaper options, you give the BGA memory chip, he gives you PC DDR Ram.
How many address lines exactly are there on the Z3 bus? I think that's 32 and therefore your fast RAM limit is more like 4GB (but that would probably be 2GB cuz you always have to have the custom chips and the chip RAM somewhere).
Actually 31, it doesnt support 8 bit reads, it reads 16bit at a time minimum, regardless wether or not only 8 bits are in use. but thats a nothing reply, yes the CPU is 32 bit and it can address 4GB total.
Take a look here: http://www.thule.no/haynie/zorroiii/docs/zorro3.pdf I bet you could avoid the autoconfig stuff and put the memory at a fixed address (or have a choice of addresses by jumper setting). Then run a utility in startup-sequence to add the memory.
Actually that card uses ZIP ram too, although adding 72 pin SIMM slots would be a piece of cake. Its a good design and if you wanted to make a memory card that is the design you should use. Upping the maximum RAM is just a matter of adding another 74257 (or 258) to get the extra address lines as the Miggy will detect how much ram is on the card.
Its also a lot easier than your BGA memory chip which would still require logic chips as CRE and ADV would have to be generated.
If you're planning to build a Zorro RAM expansion, why not build it to accept DDR/SDR? Is that possible?
It is, Xilinx have a design you can download, as do opencores I think.
All someone has to do is try... oh but they will have to add autoconfig and make sure the output bus is 68K compatiable. Also SD and DDR ram are clocked memory, the Zorro bus is asyncronous memory, its not great to mix the two busses... that said you look at 90% of Z3 boards and they are syncronous.
Get designing people.
eslapion: To sum up, designing a 72pin SIMM board would be much easier for a hobbiest to do than to start playing around with high density BGA chips.
32Meg 72 pin Simms are still available new, cheap, from most PC suppliers. Eclipse computers here in the UK sell them for £5.82 each. Make a Fastlane type board with 16 72 pin slots and you get half a gig for less than £100
