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F18A in a 99/4, possible?

9918 VDP 99/4 9918A f18a

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#1 matthew180 OFFLINE  

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Posted Sun Jan 24, 2016 8:58 PM

Does anyone have a datasheet for the 9918?  Is there any pinout difference between the 9918 and 9918A?  Also, aside from GM2, are there any functional differences?  What I am ultimately trying to determine is if the F18A can be dropped into an 99/4?  Has anyone tried?



#2 Retrospect OFFLINE  

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Posted Mon Jan 25, 2016 12:53 AM

I asked this question about two years ago and it was said at the time that the GROM's would refuse to acknowledge the F18A because the original chip hadn't 'checked in'

 

I'm not sure whether this IS truly the case or not - because if it all goes plain sailing - there will be videos of 99/4's playing Parsec and that would be awesome!



#3 Tursi OFFLINE  

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Posted Mon Jan 25, 2016 8:54 PM

I thought I did have a datasheet, but I can't find it.

I can say that the statements about the GROMs needing the VDP to "check in" are almost certainly bunk - if that were true we'd need to account for it in emulation to make the 99/4 code work, and I certainly didn't need to in Classic99. As far as I'm aware, there is no checking in possible on the 9918, you can't even identify it save explicit fingerprinting (it doesn't have an identity register, for instance).

My understanding was that it was pin compatible but I never got a chance to try it in my 99/4 before I sold it.

#4 acadiel ONLINE  

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Posted Tue Jan 26, 2016 8:23 AM

I have a 99/4 here that has a black and white display issue with its 9918.  I think I have a spare F18 that I could try in there.  Just need to the find the time to do it.



#5 matthew180 OFFLINE  

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Posted Tue Jan 26, 2016 6:38 PM

Tursi, thanks for the info.  I assumed the 99/4 could not ID the 9918, I'm more worried about some pin incompatibility.  I cannot find a datasheet anywhere, the searches are too polluted with 9918A results (most people incorrectly leave off the 'A' when talking about the IC).  I have some old IC databooks from that era, but I don't have access to them right now.

 

Acadiel, if you have time I would really appreciate it.



#6 Manic1975 OFFLINE  

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Posted Wed Jan 27, 2016 5:37 AM

I remember to read that you can expand your TI99/4 with TMS9918A but programs like Parsec or any which use new features of TMS9918A will not work. It has something to do with new registers in TMS9918A which TI99/4 will not recognize without any modifications inside TI99/4. 

This was written in one 99er. I think that someone has try to expand his TI99/4 to be able to play with Parsec,



#7 Tursi OFFLINE  

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Posted Wed Jan 27, 2016 8:15 AM

I remember to read that you can expand your TI99/4 with TMS9918A but programs like Parsec or any which use new features of TMS9918A will not work. It has something to do with new registers in TMS9918A which TI99/4 will not recognize without any modifications inside TI99/4. 
This was written in one 99er. I think that someone has try to expand his TI99/4 to be able to play with Parsec,


That's definitely not so, the addition of bitmap mode didn't add any new registers, it just added meaning to one previously unused bit. :)

You might be thinking of the 9938 update -- that requires a hardware modification to be able to access the additional status registers, as I understand it.

The best I found in my archive was a conversation I had with Sean Young about his 9918A document where the pinout listed the external video pin as "B/W", and we mutually wondered if that came from a 9918 (no A) pinout. But I think the best answer will be to really do it. ;)

#8 OLD CS1 OFFLINE  

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Posted Wed Jan 27, 2016 12:05 PM

That's definitely not so, the addition of bitmap mode didn't add any new registers, it just added meaning to one previously unused bit. :)

You might be thinking of the 9938 update -- that requires a hardware modification to be able to access the additional status registers, as I understand it.

The best I found in my archive was a conversation I had with Sean Young about his 9918A document where the pinout listed the external video pin as "B/W", and we mutually wondered if that came from a 9918 (no A) pinout. But I think the best answer will be to really do it. ;)

 

Just cram a 9918A in one and see if that works, that way the risk of burning an F18A is eliminated.  We have tons of 9918As around.



#9 matthew180 OFFLINE  

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Posted Wed Jan 27, 2016 6:40 PM

But apparently not tons of 99/4 computers around.  I don't have one to try...



#10 arcadeshopper OFFLINE  

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Posted Thu Jan 28, 2016 12:08 AM

But apparently not tons of 99/4 computers around.  I don't have one to try...


You would think there would be a bunch.

#11 Retrospect OFFLINE  

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Posted Thu Jan 28, 2016 4:39 AM

Well, oddly, quite a few will have sold in the UK, we got the TI fairly late, I think it was 1981 when they shipped.  We got the 99/4 with internal speaker and volume slider, as our TV's couldn't pick up the sound signal with the modulator they were shipping.  994a came here in '82 I think, so there should be some UK models kicking around.  Always check Evil-Bay though, as there is a US spec 99/4 with solid state badge right here.

If I could afford to do it, and had the know how, I would love to own a modded 99/4 that could play Parsec and all the Rasmus games.  For some reason I dunno I like the 99/4.

 

http://www.ebay.co.u...5gAAOSwT~9WjFKJ



#12 globeron OFFLINE  

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Posted Thu Jan 28, 2016 9:10 AM

I have a 99/4 here that has a black and white display issue with its 9918.  I think I have a spare F18 that I could try in there.  Just need to the find the time to do it.

 

Same here I can try (I have 2x different ones, 1x UK with volume slider and 1x USA without, but for 1x again the special adapter got fire a few weeks ago,

so have only 1x that works).  But I prefer to have Ksarul to give some advise, he helped me a lot to get these /4 to work  (as they came without cables and

step by step we got it to work).....I am a bit hesitating to plug in the F18A (I have spare here), I do not want to break the other /4, maybe a bit too risky.

First I need to get that odd power adapter to work. The

 

In the end I think most people will use the /4A anyway as there are so many around and have a better keyboard, are cheap etc.  

(and keep the /4's in-tact as it is?)



#13 TInaut OFFLINE  

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Posted Sat Jan 30, 2016 10:03 AM

I recall that the 9918 and 9918A are pin-compatible. The later 9118 is slightly different. I could be wrong, but I think the DRAM interface is one of the characteristic differences.

On the 99/4A, there is I recall a 74LS04 missing from the board but in the design which allows the 9918 be used instead of the 9918A.

#14 Schmitzi OFFLINE  

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Posted Sun Jul 3, 2016 7:52 AM

.

Hi,

 

some infos I´ve found for the TMS9918 VDP

 

(and some for the TMS9995 and the TMS9918A Video Display Processor)

 

zip.gif  TI-TMS9918-A--BACKUP.zip   24.97MB



#15 mizapf OFFLINE  

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Posted Sun Jul 3, 2016 10:02 AM

I recall that the 9918 and 9918A are pin-compatible. The later 9118 is slightly different. I could be wrong, but I think the DRAM interface is one of the characteristic differences.

 

Yes, the 9118 (TI-99/8) uses two 16Kx4 DRAMs (instead of eight 16Kx1 as in the TI-99/4A console), and the 9118 does not deliver GROMCLK. In the 99/8, the GROMCLK is created by Mofetta, one of the custom integrated circuits.



#16 Tursi OFFLINE  

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Posted Sun Jul 3, 2016 12:35 PM

I also pinned the VDP out via the 99/4 schematics and confirmed that the pinout is identical to the 9918A





Also tagged with one or more of these keywords: 9918, VDP, 99/4, 9918A, f18a

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