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Prototype 1000 TX Motherboard

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dlightman

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I had the opportunity to acquire a prototype 1000 motherboard that was unpopulated; I thought it'd be something cool to hang on the office wall.
Aside from not having a few part numbers it's identical to production TX motherboard, but it appears to have an interesting twist in the form of a 16-bit slot.

What do you guys think?

Large photos here: https://imgur.com/a/Z3N8WEr

Front:
DfjJAlu.jpg

Back:
FHxq9o7.jpg


Production TX motherboard for comparison: http://www.oldskool.org/guides/tvdog/images/TXAllOutLarge.jpg
 
Thats neat. The 16 bit slot (the small part of it) doesnt appear to have traces.
 
Yep it doesn't appear to have any traces at all. Also for the revision it says PP1 which I'm guessing stands for pre-production 1. I wonder what it's purpose was. To show that a 16 bit slot could have fit? Maybe the small part of the slot would be tied to the proper places with wire later? It's interesting for sure.
 
dlightman said:
Yep it doesn't appear to have any traces at all. Also for the revision it says PP1 which I'm guessing stands for pre-production 1. I wonder what it's purpose was. To show that a 16 bit slot could have fit? Maybe the small part of the slot would be tied to the proper places with wire later? It's interesting for sure.
Click to expand...

I counted the pins, and its 18x2. I thought that part was 19x2. I could be wrong though.
 
18x2 is correct (62 pins vs 98 ). Not sure where they'd have provided the high IRQ's and additional DMA channels though. Seems more of a exercise in placement?
 
Trixter said:
Very cool, and a very rare item. I'm surprised there was a single 16-bit slot -- I wonder why they removed it later.
Click to expand...

The Tandy 3000 HD and HL were on the market in 1987 when the TX design was being finalized. They were the 'business' class AT compatibles from Tandy. I suspect they didn't want the cheaper TX to compete.
 
The 16-bit slot wouldn't have been useful without significant redesign of the system to implement high IRQs and high DMAs -- something Tandy didn't do until the very tail end of the 1000 era, with the 1000RSX.

Also in 1987, a lot of 16-bit ISA cards were full-height and full-length and wouldn't have even fit in the 1000TX's case! So I think the slot was probably just for diagnostic testing of the prototype, and was never intended to be included in the production model.
 
My guess would be it was meant to be single purpose - such as a memory expansion card. But people would have expected a 16-bit ISA slot to be AT compatible, so it was dropped.
 
That's a fair assessment: The Olivetti M24/AT&T PC 6300/Xerox 6060 have the same 16-bit proprietary slot for the same reason (memory expansion, although I've seen just as many "fill motherboard to 640k" boards for this slot as I've seen EMS 3.2 (1986) boards).
 
Anything's possible but consider that the 1000 TX's base memory could have been upgraded to 768k using the 24 DIP sockets located just before the ISA slots.
 
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Was there ever any exploration of the 16-bit extended slot on this board? Did you check continuity with the 12v/5v/ground lines to see if it's just unused vias, or possibly actually connected?
 
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