TI-990 ...chip sources

James B. DiGriz jbdigriz at dragonsweb.org
Mon Oct 8 23:53:42 CDT 2007


Chuck Guzis wrote:
> I've done a little digging and, in addition to the SBP9989 I2L 
> bipolar CPU, TI evidently produced something called an SMJ68689GBM, a 
> CMOS version.  Supposedly used in defense apps such as TOW missles.
> 
> Anyone ever seen one of these things in the flesh?  Supposedly, DOD 
> bought up all remaining stocks as spares.
> 
> Cheers,
> Chuck
> 
> 

According to Jim Krych, who is currently spearheading a revival of the
SAMS mapped memory expansion for the 99/4A over on the swpb list at
yahoo, the 68689 is faster than the 9989, but it wasn't enough
improvement for military projects being coded in ADA, not when PPCs, 
Sparcs, et. al. were at hand. There was "lifetime-buy" by the DoD, but 
most of the weapon systems that used the 9989 or 68689 have been 
expended or replaced by now anyway, I would think. At any rate, you can 
find either one, and the SBP9900, as well, through partminers and other 
brokers.

How much faster, though? It's a static design running DC-16Mhz according 
to the datasheet* I have. Uses a 16-bit data bus and does have the full 
9900 instruction set, plus signed multiply, signed divide, load WP, and 
load ST. No internal scratchpad RAM like the 9995 for use as a register 
file or stack, though. There is an attached processor interface and 
locking mechanism as with the 99000, though.

On the 8-bit 4A expansion bus, a 9995 (as in the Myarc Geneve) runs up 
to 5-6 times faster than a 9900, partly due to the 256-byte scratchpad 
ram, and partly due to instruction pipelining. The Geneve uses a 12Mhz 
oscillator, but it's still the same 4-phase clock arrangement as the 
9900, just generated internally, so it's actually running with the same 
cycle time as the 9900. It would be more accurate to call it a 3Mhz 
processor. It just feels like about a 10-12 Mhz '286 AT in actual use. 
They've been over-clocked too, at 16-18 Mhz, with few problems reported, 
aside from timing issues in software.

Some might consider the 99000 chips, the microprocessor versions of the 
990/12 CPU as used in the 990/10A, BS300, and so on, to be more 
interesting, whether in a mini, a desktop, or a console. Also, for a 
while there was an open core project called the Freedom CPU which 
started out at least as a 32-bit derivative of the 9900, with Sparc 
influences. Need to check back into that.

jbdigriz

* ftp://popeye.dragonsweb.org/pub/ti/sgus015.pdf, courtesy of Berry 
Harmsen of the Dutch TI User Group



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