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Better cpu

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A drop in replacement would be 100% compatible only faster. That's what we're looking for in this thread, right? I agree it wouldn't make sense to replace the CPU with an incompatible one. 

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Some folks have overclocked the 9900 to 4MHz.

Thierry has info about doing that:

http://www.unige.ch/medecine/nouspikel/ti99/clockup.htm

 

There was the SBP9900 which goes to 4.4MHz

http://www.cpushack.com/2015/02/05/ti-tms9900sbp9900-accidental-success/#more-19685

 

I think this is the 4Mhz rated S9900 part for $20 here

http://www.unicornelectronics.com/backcorner/ic.html

 

 

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If my TI was younger and my primary daily driver, I have to admit it would have been intriguing enough to contemplate.  I'm chicken though, because with this antique gear, I'm a little leery about overclocking, overheating and damaging it.  Now I have to admit, I do not want to play games on a faster computer, because I suck bad enough as it is on regular speed games. 🙄    Having the ability to toggle it down to normal would be a requirement, but that's more soldering and holes being drilled.  Now when it comes to other programs I use, and for how little I use them, the speed difference would not really be that big of a deal.  It might even add incompatibilities with some programs, like communications programs.

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13 minutes ago, carlsson said:

Matt Sarnoff designed this system in 2010:

 

 

http://www.msarnoff.org/6809/

 

I would love to add 16K more VDP memory to the TI99/4A 9918 chip, that would make RXB really better with 32K VDP memory instead of just 16K 

Also he is not using DRAM which is also very cool.

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I guess it is easier to use SRAM to expand the memory. DRAM requires refresh, and 32K cannot be addressed by the 9918/28, so you'd need some bank switch, and some idea how to refresh the switched-out 16K.

 

Edit: Of course, this is only half the truth; you have to do some address latching for the SRAM. DRAM is addressed in two passes; the row and the column (using the RAS and CAS lines). Hence, DRAM chips only have half of the address pins. So when you replace DRAM by SRAM, another circuitry is needed to rebuild the address.

Edited by mizapf
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The way I added 16-bit wide RAM to the machine not only speeds up memory access to the normal memory expansion. It also adds another 32 K RAM, which can be paged in, in 8 K chunks, across the rest of the address space as well. In addition, the fast 32 K RAM expansion can be paged out, to still allow access to the normal memory expansion in the box.

So this modification increased CPU-addressable RAM from 32 to 96 K. Today, when we large RAM-disks, and interfaces to SD-cards with Gigabytes of storage, this is nothing. But when I invented the design back in the mid 1980's, it was quite a large memory for a home computer. The first IBM PC could be bought with 16 K RAM in 1981...

 

As an example, I could page in RAM to get a contiguous RAM file in addresses 0000H-7FFFH. That means monitor ROM, DSR and command module ROM is paged out, but frequently you can do some meaningful actions without them. With this setup, you have access to a 16 K words array, which can be directly addressed by the CPU, to use for internal sorting or whatever. Then just page the RAM out again, and any normal activity in the computer can't touch your array.

Edited by apersson850
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Hm, are you building the TI-99*4 where the multiplication sign indicates it has multiple cores and the 4 will mean you've built a quad-core system?

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This topic reminded me of a picture over at the nightfallcrew website from a while back, something you can do with your old cpu....

 

TMS 9900 CPU Key Ring

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By the way, is this article by Walden C. Rhines (2017) old news to most people over here?

https://spectrum.ieee.org/tech-history/heroic-failures/the-inside-story-of-texas-instruments-biggest-blunder-the-tms9900-microprocessor

 

Also a TMS9900 cost $70 in 1978. Of course it must've dropped in price quite a lot by 1983 but it still would be a reasonably expensive key ring back then.

Edited by carlsson

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DonO and GaryB made a working accelerator board based on the TMS99105 for the 99/4a console.

Maybe they would be willing to share their schematics as a jumping off point for the interested.

 

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13 hours ago, dhe said:

DonO and GaryB made a working accelerator board based on the TMS99105 for the 99/4a console.

Maybe they would be willing to share their schematics as a jumping off point for the interested.

 

Didn't they halt that because the traces were so close, on the PCB, as least for technology at that time, that they were were having some kind of signal interference between the traces?

 

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I don't know if anyone knows the TMS320 family.. but their is a host processor at 60Mhz. And I'm sure other speeds. But I think, and I'm not a CPU guru, but I think it would make a great team with the ti-99

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4 minutes ago, GDMike said:

I don't know if anyone knows the TMS320 family.. but their is a host processor at 60Mhz. And I'm sure other speeds. But I think, and I'm not a CPU guru, but I think it would make a great team with the ti-99

The TMS320 series is actually related to the TMS9900 series, so it does make a nice pairing from a warm fuzzies point of view. 

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Somewhere, and I just can't find it now, but I've seen an ad for a version of the 320 and they called it a host processor that accepts instructions off-load through serial bus and memory was shared blah blah...I'm not an engineer, but it seems like a not so hard thing..kinda sorta

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It's related, but it's not compatible. Not electrically, and not software-wise either. :)

 

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On 3/1/2020 at 10:15 PM, GDMike said:

Ok, if someone could put like, 4 ea 9900s on a board and shared memory...oooh

Actually, someone did build a 16-processor parallel computer using TMS9900s about ten to fifteen years ago. I'm pretty sure the website documenting it is gone now, unfortunately.

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2 hours ago, Ksarul said:

Actually, someone did build a 16-processor parallel computer using TMS9900s about ten to fifteen years ago. I'm pretty sure the website documenting it is gone now, unfortunately.

I went poking around for that, and found this instead. (PDF on a .mil site.)

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5 hours ago, Ed in SoDak said:

Wow! The ultimate TI shoot-em-up game. Fire real Redstone rockets!

Also the absolute best Missile Command clone.

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