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fabrice montupet

99/4A Programs Compatibility with the V9938/58

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This topic is made to point on the 99/4A programs made for the TMS9918A/9929A and that have some compatibility problems with the Yamaha VDP 9938/58.

 

My computer for the test is the Tiny-99/4Av3.

- In a previous message, I talked about the "Copper" demo program that is specially made for the 9918A/29A and that doesn't work with the Yamaha VDPs. Maybe, one day, a compatible version will be create. I hope!

- Sabre Wulf didn't work with the V9938/58 but Rasmus recently corrected the problem by giving the new version of the game.

- Today, I have tested the Mega Demo "Don't Mess With Texas".  At the beginning all works fine but the problems arrive at the "Wolfenstein alike " demo: I perceive what it should be displayed (as the gun) but  the screen is filled with garbage, the following demo with scanlines effects doesn't work well (no moving texts appear)  and the demo with red/green/white waves crashes the computer. Someone that also has a V9938/58 upgrade on his 99/4A could test the MegaDemo too? To tell if he encounters the same problem.

 

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Posted (edited)

I have tested Q*bert from Parker Brothers (FinalGROM99 and real cartridge) : No image, black screen only. However I hear the game working (sounds OK and I can play blindly). Please, can someone confirm?

Edited by fabrice montupet
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I confirm by myself with a TI-99/4A and a Mechatronic 80 columns sidecar expansion attached:  The problems have also been observed, with strictly the same symptoms.

 

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The Q-Bert problem is a quick fix that has been known since the Geneve came out. Video Chess and TI Logo also have V9938-related patches. I remember making these changes back around 1989 or so for these while I was in Germany. I don't have the source information handy, but I'm pretty sure it appeared somewhere in Micropendium back then.

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Thank you Jim!

I found the Micropendium article (in mp9512). The modification consists of changing the bytes >02808800 to >02808700.

Now Q*Bert is working fine :-)

 

 

 

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Posted (edited)

Nonogram and Minesweeper from Sometimes99er are incompatible. The games are playing but there's garbage on the screen.  Hope that a fix will be made! Theses games are so cool.

EDIT: the Parallax Starfield demo doesn't work too.  All of them displays the same garbage... same VDP register initialization problem.

Edited by fabrice montupet
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I wonder if most issues could be resolved by running something first that initialized registers and VDP RAM to a 9918A compatibility state before loading the programs?

 

Hoping to get patches from authors that don't have 9938 equipment seems like a losing proposition.

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The 99/4A GROM0 system is already patched in the startup sequence to be 9918A/29A VDP registers compatible with the V9938/58 (Without that the computer would display garbage on screen).  But, afterwards,  if a program re-sets again the VDP registers without the good values, the display goes wrong. This is why I think that the non working programs should be patched.
That said, I can understand that their authors can't have time (or the desire) for that. But I would be so happy to see them working on a V9938/58 based TI-99 computer.

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