ISA 16 bit memory card project?

[mac512]

Hi there!

First things first: I'm completely noob in this posting thing. I've published this same post but in the WiKi section for hardware, so if someone can help me correct or erase that post i'll appreciate it.

Now, back to bussiness, i would like to know if there is such a project going on in the vintage computers space. As usual, memory cards are scarce and going up in price. Not to mention that old cards with tons of diyng memoriy chips ... so a small card with even just one simm sounds useful ...

Thanks.

Jose.

 

[pbirkel@gmail.com]

See the boards/activities at: http://www.s100computers.com/ ?

Board-list: http://www.s100computers.com/My System Index Page.htm

RAM board: http://www.s100computers.com/My System Pages/RAM Board/4MG RAM Board.htm

 

[pearce_jj]

8-bit ISA RAM expansion board would be very simple I think. Could probably even add the logic to an XT-CF card.

Eg with a 4 Mb Static RAM chip: http://uk.farnell.com/alliance-memory/as6c4008-55pcn/sram-4mb-2-7v-5-5v-512kx8-pdip32/dp/1562900

 

[Simone2013]

XT-CF card with 4Mb SRAM AS6C4008 would be fantasti & cheap! anyone has done it before? schematics?

 

[nestor]

8-bit ISA RAM expansion board would be very simple I think. Could probably even add the logic to an XT-CF card.

Eg with a 4 Mb Static RAM chip: http://uk.farnell.com/alliance-memory/as6c4008-55pcn/sram-4mb-2-7v-5-5v-512kx8-pdip32/dp/1562900

But what is the point of a 8 bit memory card? A 4 Mb (512 kilobytes) expansion could be useful in a motherboard with 128 KB onboard, or maybe a bit more using part as UMB.

A 16 bit memory card is more complex, for example using at least four 4 Mb SRAM chips could provide 2 MBytes of XMS.
EMS is another story, too difficult to implement it

 

[pearce_jj]

But what is the point of a 8 bit memory card?

A low-cost board providing solid state storage and RAM expansion all in one - sounds good to me

 

[sergey]

I see two distinct uses for a 8-bit memory card:
1. Adding low memory to 640 KiB (e.g for 5150 systems with 256 KiB on board)
2. Providing UMB (or even some kind of EMS).

It might be possible to implement a board that will do 1 and 2. But it will require a bit more complicated address decode / memory mapping logic than needed for 1 or 2 alone... I can probably come up with something, but I don't have much need in such a board. (While I do have a 5150 and Retro-PC motherboards, they work good enough with 256 KiB for my needs). So I guess the question is how many people are interested in such a card, and in what scenario - 1, 2, both 1 and 2?

As for 16-bit memory cards - I personally don't see much need in those. Most 286 and later systems support more than 1 MB on-board anyway. And IMHO for older 286 systems (e.g. IBM AT) adding such a card is a kind of cheating
Also 8-bit card will work in 16-systems... it just will be slow...

 

[pearce_jj]

By using a 1MB sRAM, the addressing issue is greatly simplified How does EMS work, presumably a page register and a mapping window?

 

[sergey]

By using a 1MB sRAM, the addressing issue is greatly simplified

But then you throw away some of SRAM... it is cheap but feels wrong

How does EMS work, presumably a page register and a mapping window?

Something like this. If I remember correctly newer versions of EMS required two mapping windows.