Jump to content

Recommended Posts

From their documentation:

 

Quote

This small adapter board can unlock the potential of many 8-bit systems from the 1980's including the Colecovision, MSX, SG-1000, SC-3000, TI-99/4, Memotech MTX, and more. Instead of the original output—often wavy, blurry RF with color fringing—soldering this tiny board directly to the back of your graphics chip will enable clean RGB output, ready to be sent to your favorite line doubler (like the OSSC), RGB monitor, or upscaler (like the Framemeister).

 

Share this post


Link to post
Share on other sites

For completeness: we haven't tested compatibility with any other systems besides Colecovision yet, though there isn't anything Colecovision-specific in the circuit.  My confidence is high that it should work anywhere the '992xA series VDP has been correctly integrated.  Better news: I have seen the exact same mod board working on both an NTSC and PAL system without any changes.  So that seems to bode well for compatibility, too.

 

If anyone decides to try it with a TI-99 or otherwise, it would be great to hear about positive (or negative :D ) results!

 

As for that list in the documentation, I did my best to track down which products in the 80's used the '9928.  It's tricky because there seems to be a lot of (slightly) incorrect information out there.  (E.g., I've seen Colecovision described on more than one website as having a '9918 which has never been true as far as I know.)  You guys would know a lot better than I would: was I correct in listing the TI-99/4 as using a '9928A?  Thanks!

  • Thanks 1

Share this post


Link to post
Share on other sites
1 hour ago, Falonn said:

was I correct in listing the TI-99/4 as using a '9928A?  Thanks!

For the U.S. Version it was the TMS9918.  My memory is not what it used to be, so I cannot remember if the European PAL version used a different version or not.

 

Was this thing developed because the other product was no longer available?

  • Thanks 1

Share this post


Link to post
Share on other sites
7 hours ago, Omega-TI said:

Was this thing developed because the other product was no longer available?

Do you mean the ColecoRGB?  There is a more complete version here, but the shorter story is that all three or four of the widely-known circuits had at least one problem.  Almost all of them suffered from the "too much blue" problem (due to an interesting choice on TI's part when designing the VDP) and pixels that are too narrow when coming from black (making text very hard to read) was a problem unique to ColecoRGB (among others).

 

TMS-RGB combines the strengths of each while working around the weaknesses of each.  You don't need an oscilloscope during install anymore to tune the colors, etc.

  • Thanks 1

Share this post


Link to post
Share on other sites

Not the "A" version for the 99/4, at least for the 9918.  I do not know if there are non-A versions of the 9928A and 9929A.

 

EDIT: While working to confirm or deny, I found some things in the Wikipedia article for the TMS-9918 which could be cleaned up:

 

Screen mode 2 details

[...]

When manipulating the screen in BASIC with the LINE command, one easily could exceed the maximum 2 colors per 8×1 area[...]

 

What LINE command in what BASIC??

 

Scrolling

The TMS9918 does not have any scroll registers, and so scrolling must be done by software. Furthermore, scrolling can only be done on characters boundaries.[citation needed]

 

Citation needed, indeed.  Pretty certain this assertion is well debunked.

 

Share this post


Link to post
Share on other sites

Too bad Wikipedia has a rule against Original Research;  You will need to publish documentation showing this is false, THEN get it well circulated for a credibility score, THEN get SOMEBODY ELSE to battle with the page maintainer to make the correction and add the citation.

 

 

Share this post


Link to post
Share on other sites

The LINE command is from some other BASIC; there are some machines apart from the TI that use the 9918A. The "Furthermore" sentence is wrong and should be removed completely (update comment "scrolling possible by tile scrolling, pattern updates"). This is not a matter of original research; the wrong claim is just removed.

  • Like 1

Share this post


Link to post
Share on other sites

hmm.. I suppose just linking to any of Rasmus's fine titles that make use of this method on the 99 would be sufficient citation. Still, I have heard too many horror stories about trying to get a simple correction in edgewise on curated articles.

 

It's worth a shot; there are many examples in the wild of this being done that could be pointed to.

Share this post


Link to post
Share on other sites

Hmm, that sounds like there are about three votes for the TI99/4 not having a '9928A.  Should I remove it from the list on the mod's front page?  That was the machine I was the least sure about while trying to find things that used it.

Share this post


Link to post
Share on other sites

I believe it is true of the 99/4a in PAL land, but not the kingdom of NTSC.

In America, TI used a 9918a that directly outputs composite video.

 

The 99/4 with no a used a 9918, not a 9918a. Not sure on the PAL-land situation there.

 

Share this post


Link to post
Share on other sites

For a more complete note on VDPs and the TI computers: The TI-99/4 (1979-1981) used the TMS9918, and was only released as an NTSC machine. The TI-99/4A (1981-1984) used the TMS9918A in NTSC land and the 9928A/9929A pretty much everywhere else. There were also mods for the NTSC machines to replace the video chip with a 9928A to get RGB capability. The TI-99/8 used the TMS9118, as did the Tomy Pyuuta/Tutor line. The Powertran Cortex could use the 9918A, 9928A, or the 9929A, IIRC.

  • Like 1
  • Thanks 2

Share this post


Link to post
Share on other sites
16 hours ago, Falonn said:

As for that list in the documentation, I did my best to track down which products in the 80's used the '9928.  It's tricky because there seems to be a lot of (slightly) incorrect information out there.  (E.g., I've seen Colecovision described on more than one website as having a '9918 which has never been true as far as I know.)

Oooooh yeah. There's a tendency to write everything in the family down as 9918 or 9918a. From a specs and programming point of view, this is even accurate.

...

And then you flip a coin to determine if the writer writes "9918a" for both the a and non-a families, or writes "9918" for both. Of which neither approach is right in any way.

Share this post


Link to post
Share on other sites

I don't know if you can come up with enough 9918-NO-A chips to be worth even considering anymore... ;)

 

Share this post


Link to post
Share on other sites

Thanks for the clarifications, everyone.  I think it'll be better if I remove it from the list.  I'd rather have the PAL version be covered by the "and more" at the end of the list than have some unsuspecting NTSC TI-99/4A user go to the trouble of building or buying one of these things just to find out it won't work for them.

 

Eventually as more of these RGB boards make their way out into the wild, the right answer will be to add an "actually tested on" compatibility list as those reports come in.  In the meantime, it's better to be safe than to inadvertently make someone else sorry.

 

Thanks again!

  • Like 2

Share this post


Link to post
Share on other sites
10 hours ago, OLD CS1 said:

Citation needed, indeed.  Pretty certain this assertion is well debunked.

In the most naive sense, that is exactly right.  There is no pixel scrolling.  If you want to do so, you need to write multiple pattern maps into the RAM and switch between them.  But due to limited memory, this also limits the total number of unique tiles you can use.

Share this post


Link to post
Share on other sites
8 hours ago, JB said:

I believe it is true of the 99/4a in PAL land, but not the kingdom of NTSC.

In America, TI used a 9918a that directly outputs composite video.

 

The 99/4 with no a used a 9918, not a 9918a. Not sure on the PAL-land situation there.

 

As far as I know, there was never a 9919 or the like.  So PAL equipment had to do their own composite encoding.

  • Like 1

Share this post


Link to post
Share on other sites

I want to say that I /also/ found evidence years ago that the 9919 - a PAL VDP with composite output - was at least specified. But I can't remember now why I think that.

 

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...

  • Recently Browsing   0 members

    No registered users viewing this page.

×
×
  • Create New...