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Tandy 1000HX on eBay with aftermarket RAM?

Tandy's card used a custom chip for DMA and logic, four 64K x 4 DRAMs and eight 256K x 1 DRAMs. That got you 384KB. This board is using a true 8237 DMA chip, lots of discrete logic and four 256K x 4 chips, which gives you 512KB. The extra memory probably is not used, and certainly not usable like in a Tandy 1000 TX.
 
You need that DMA enabled card to be able to use any of the other PLUS cards that stack on top of it. They are worth having (have one in my 1000HX).
 
Unknown_K said:
You need that DMA enabled card to be able to use any of the other PLUS cards that stack on top of it. They are worth having (have one in my 1000HX).
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This aftermarket card does have DMA... just not the Tandy ASIC. Instead it has a real AMD 8237 and glue logic along with the RAM.
 
I think what he's saying is you need it for the connector stack. That after market card only has the one shrouded male header. So you can't stack a third card with it where as you can with the genuine Tandy part.

One of the reasons I haven't done a PLUS card design yet is the inability to source those tall male headers. Incidentally the stacking height is the same as PC-104. It should be possible to build a PLUS to PC104 adapter card in the lower slot then stack 104 cards in slots 2 and 3. Just a thought.
 
eeguru said:
I think what he's saying is you need it for the connector stack. That after market card only has the one shrouded male header. So you can't stack a third card with it where as you can with the genuine Tandy part.

One of the reasons I haven't done a PLUS card design yet is the inability to source those tall male headers. Incidentally the stacking height is the same as PC-104. It should be possible to build a PLUS to PC104 adapter card in the lower slot then stack 104 cards in slots 2 and 3. Just a thought.
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Are you talking about the pins in this photo ? : http://www.oldskool.org/guides/tvdog/images/HXMemoryCardTopLarge.jpg

Perhaps the better solution would be to design a three card solution with normal sized headers in zig-zag alignment. The first card would add DMA and RAM, and would be easy enough to do as shown in the first picture. This card would only have the one pin header sticking up. The second card would contain a serial port, something the Tandy is truly lacking. If there is space available, perhaps a second serial port or a good parallel port can be added. This card would also have a one pin header sticking up. The third card should be for an XT-IDE solution, and considering the space constraints it should have a CF slot.
 
It's not a matter of it not existing. I'm sure a lot of companies made or make it. However I can't find it readily available through a distributor and I hate searching Chinese brokers to source 50 of them - especially something like this with a very ambiguous name.

If someone can find a part number and distributor with stock, I'd be happy to build some plus cards.
 
Unknown_K said:
What kind of PLUS cards were you planning on making (Ethernet maybe?)?
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If anyone wants to make an ethernet PLUS card I'll buy one!

There were actually a lot of aftermarket PLUS cards in the early 90's. I have one with expanded memory and 2 SIMM slots for a ram disk. I think it needs some kind of proprietary driver so when I have time (Haha, right) I'll try to get it working.
 
Ethernet + microSD + RAM + RTC would be a very useful card - especially if it offered the stacking connectors. Certainly do-able.

I regret not adding Ethernet to the PCjr card.
 
I have an ram expansion on my EX that includes DMA. Rigged up a 8 bit ISA slot to it (lots of wires and a couple IDE type connectors), and added an XT-IDE with compact flash. Works just dandy!
 
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