Seeking... TI TMS9902 ICs

Sean Caron scaron at
Sat Jan 3 11:25:30 CST 2015

OK, back story, I'm particularly interested in the TMS9900 because my dad
used TI 990 machines in some way in his first job out of school at Chrysler
(maybe as a CAE machine and embedded development platform for early auto
electronics he was working on?) so, growing up, poring through the
bookshelves, I would stumble across documentation for this "strange" TI 990
system and I've always been kind of intrigued by it... I've never seen a TI
990 system in the wild, and only a few folks are displaying 990
architecture SBCs or actual TI-990 systems so the obscurity factor is there
a little bit... Last but not least the architecture is somewhat unique and
the instruction set is nice.

I was visiting my parents over the holidays and, being the more
historically inclined of the two of us, offered to help my dad get rid of
some old obsolete "ephemera" ;) So, amongst a fairly huge "data dump", my
dad set me off to start with a large binder left over from an introductory
seminar on the 990 from the 70s and a few ICs from his junk box...
TMS9901s... we couldn't find any CPUs for some reason though my dad was
certain he had a few kicking around somewhere. We'll look again next time I

I did some research and it seems that straight TMS9900s are hard to find
(and harder to find cheap) and they are frustrating to work with because
they require three different voltages to operate, and four clocks (ideally
supplied by the equally difficult to find TIM9904). So,  I'm with you, I
did decide to use the TMS9995 to do my 990-architecture machine. (I'll just
use my stock of DIP 68000s when I want to build something with a 16-bit
data bus...)

The reason I asked here is that I'm really wary of the parts from China and
Hong Kong, I have read a lot of stories where people have bought these ICs
and they have turned out to be completely re-marked, totally bad, somewhat
defective, etc. I'm trying to find a local source if I can... I was able to
source the 9995s locally from a guy here in MI... I got the 9901s from my
dad. Just need a few 9902s and I should be ready to roll... if I get
desperate I might try the China suppliers but I'd rather get it from a list
member, or at least an onshore eBay seller.

Has anyone bought ICs from one of these Chinese suppliers and found that
they were bona fide and in general functional (I know, now 100% guarantees
on random old ICs...)? I'd be very interested to hear endorsements. The
offshore sellers have a lot of interesting old ICs and the prices are in
general very low... I would go to town if I felt safer, LOL.

I have seen those parts kits you mention and I have wondered about them as
well... I assume they are targeted at guys like me, people trying to build
home brew 990 machines? I do wonder about the origins... I could believe
they were maybe 99/4a machines at some point in time sent overseas to be
scrapped, with the remainder... the EPROM, SRAM and glue, made up from
other sources. However, I've closely scrutinized a picture of the 99/4a
motherboard and I don't see a TMS9902 on there so it might not be so easy
to just say, oh, someone pulled all the bits off a 99/4a and threw some
extra stuff on top; I'm just not sure.



On Sat, Jan 3, 2015 at 10:55 AM, Al Kossow <aek at> wrote:

> On 1/2/15 2:53 PM, Sean Caron wrote:
>> Hi all,
>> I'm looking to pick up a few TI TMS9902 ICs
> they don't seem to be difficult to find
> there seems to be whole kits of 9900 parts there
> If it were me, I'd use a 9995 instead of a 9000 though
> I wonder what this is a kit for?
> The whole system seems to be there, including two memory mappers?

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