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cbmeeks

Any modern TMS9995 projects lately?

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I've been looking over the TMS9995 recently and was wondering if anyone is working on anything new with it?

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Nothing new ... but have been having an e-mail chat with a chap helping to restore a Royal Observer Corp Group HQ Bunker in Scotland (that's the northern bit of the UK!). This is one of a number of HQ Bunkers that would receive information from smaller 3-man underground bunkers about the spread of nuclear fallout in the UK in the event of someone dropping one or more nuclear bombs on us. Operational up to the early 90's. They've got a number of bits of kit that use the TMS9900 and 9995 that they're restoring, and they were after one of my TMS9900 PCBs to use as a simple way to test their processors and clock chips.

 

https://www.facebook.com/28Group/ if you're interested. It's a Facebook page but if you haven't got an Facebook account just click the "Not Now" link towards the bottom right of the login banner displayed and you can scroll through to your heart's content and try to spot our favourite processors.

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Oh wow.  That's awesome!  I will check that out later (can't FB at work). 

 

So I found a TMS9995ANL in my bin of CPU's.  I have no idea if it's legit.  I tried some IPA and hard scrubbing to see if anything came off (nothing did).  So I thought I might try and wire-wrap a small prototype board.  Unfortunately, I don't have any serial chips in the TMS family (9902 IIRC).  So I may order one of those.  The problem there is that there is no guarantee it will be legit either.  Which sucks.

 

I wonder how hard it would be to use a UART I'm more familiar with?  Like a 65C51? 

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6 hours ago, cbmeeks said:

 

So I found a TMS9995ANL in my bin of CPU's.  

 

 

 

In my experience the quickest way to test that your found 9995  is working, in wire wrap, is to add 1 EPROM, a LS138 decoder, and the SN76489 sound chip.

 

Take some 99/4A sound or music-playing code - change the WS pointer and the >8400 pointer and it should run. (Oops, I forgot that I used the 60Hz VDP interrupt and INT1.. you could use a simple delay loop at least. Or test the internal timer.)

 

I felt more confident after executing a program that writes sound list bytes to one address.

 

Then move on to 9902 since you know that code executes correctly. Plenty of sample code is out there. Here's Thierrys documentation and sample code.

 

If you need a new 2x20 wire wrap socket, I got this batch from eBay shipped from Canada, about $3 each. (I can share these and  9902.)

 

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@FarmerPotato that's an excellent idea!!  In fact, I know for a fact I have some legit SN76489's.

 

Thanks for the suggestion.

 

Keep in mind I have never programmed 99xx assembly so I may have more questions.  🙂

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Qq on this... could you simply put a 9995 in place of the original processor for the TI-99/4a?

I do not know the ins and outs as you veterans do of architecture or the full functionality of the TI processor.

Merely curious. And thanks.

Sent from my SM-G955U using Tapatalk

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4 hours ago, Mehridian Sanders said:

Qq on this... could you simply put a 9995 in place of the original processor for the TI-99/4a?

I do not know the ins and outs as you veterans do of architecture or the full functionality of the TI processor.

Merely curious. And thanks.

Sent from my SM-G955U using Tapatalk
 

No.

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5 hours ago, Mehridian Sanders said:

Qq on this... could you simply put a 9995 in place of the original processor for the TI-99/4a?

No way. Different pin count (9900 has 64 pins, 9995 has 40), 9995 has internal data bus multiplexer (8 bit data bus), address bus (9900 has 15 lines (no A15), 9995 has 16 lines), 12 MHz external clock, different interrupt inputs, ...

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Don't worry, questions are there to be asked, and we are here to learn. :) Feel free to ask. My reply was not supposed to convey anything about your question, apart from the technical facts.

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The TMS 9995 also has internal 16-bit memory high up in the memory map. The TMS 9900 doesn't. In the TI 99/4A, this area is used for memory expansion. In a computer based on the 9995, the equivalence of the RAM PAD at 8300H would have been located in this internal memory.

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On 2/18/2020 at 12:59 PM, Mehridian Sanders said:

Thanks guys. I will ask more informed questions in the future, sorry. 🙂

I worked for a guy who always said "The only stupid questions are the ones you didn't ask"

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