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Great Hierophant
November 3rd, 2008, 09:49 PM
I am wondering how compatible the Tandy video chips are with the true IBM Color/Graphics Adapter. Here are some tests to throw at it:

RGB Tests

1. Games that use tweaked text modes as graphics modes

2. Changing Intensity in 4-color palette modes

3. Support for green/red/brown and cyan/magenta/white palette

4. Changing border color in text modes

5. Changing foreground color in 620x200 mode

6. Support for the red/cyan/white palette

7. Games that change the palette in mid-frame

8. Blink attribute/16 background colors in text modes

As I understand, there seems to be the Video Array Chip found in the Tandy 1000, A & HD, a revision for the SX, EX, HX (#2684), another for the TX (Big Blue) and RL/SL/TL (Tandy Video II).

Composite Tests (1000, A, HD, SX, EX, HX & TX only)

1. Black and White Output in Modes 0, 2, 5 and 6.

2. Color Output in Modes 1, 3, 4 and 6 with color burst enable

3. Same color and black and white displayed colors as CGA

In all cases, deviations from the IBM standard should be documented.

Mike Chambers
November 5th, 2008, 06:11 AM
of course i haven't done all these tests on my 1000TX or 1000HX, but everything seems to work perfectly that i've tried as far as CGA.

Trixter
November 5th, 2008, 12:55 PM
This is from memory of a year ago when I last had my Tandy 1000 set up, so if you want to trust my memory:

RGB Tests

1. Games that use tweaked text modes as graphics modes: YES

2. Changing Intensity in 4-color palette modes: YES

3. Support for green/red/brown and cyan/magenta/white palette: YES

4. Changing border color in text modes: YES

5. Changing foreground color in 640x200 mode: YES

6. Support for the red/cyan/white palette: YES

7. Games that change the palette in mid-frame: There are only a few games that do this; the most common one is California Games, and it does a speed test to determine if it should do it or not. That test works on the Tandy 1000 but does not work on any other Tandy (due to various things like 8086, or NEC V20/V30, or 7.16MHz, etc.). So yes, with caveats.

8. Blink attribute/16 background colors in text modes: YES

You forgot to ask about MC6845 stuff, like shifting the screen left/right/up/down or custom video modes like 256-pixel-wide modes, but the answer to that is YES as well.

Composite:

1. Black and White Output in Modes 0, 2, 5 and 6: YES

2. Color Output in Modes 1, 3, 4 and 6 with color burst enable: YES

3. Same color and black and white displayed colors as CGA: YES for the red/green/yellow and cyan/magenta/white palette with all background colors and intensities. I have *NOT* tested -- or do not remember if I have tested -- custom colors in 640x200, or the cyan/red/white palette. Due to the nature of how cyan/red/white is turned on, I would highly doubt it works.

BTW, it is interesting to note that the answer to #3 above (same colors as CGA) is NO for original IBM CGA. When I was testing 8088 Corruption, I was surprised to discover that 40x25 textmode has slightly different colors than expected (I don't mean everything was off by a hue, I mean that some colors were exact and others were quite different).

Great Hierophant
November 5th, 2008, 01:33 PM
You forgot to ask about MC6845 stuff, like shifting the screen left/right/up/down or custom video modes like 256-pixel-wide modes, but the answer to that is YES as well.

Indeed, however, as the Tandy 1000 uses a real MC6845 CRT controller, I doubt there would be any incompatibility. I wonder, however, if they would work on those Tandys that incorporate 6845 functionality into VLSI components (everything with a suffix.) Also, as there are slight differences between the Tandy's font and IBM's font, games that use the tweaked text modes may appear ever-so slightly different.


7. Games that change the palette in mid-frame: There are only a few games that do this; the most common one is California Games, and it does a speed test to determine if it should do it or not. That test works on the Tandy 1000 but does not work on any other Tandy (due to various things like 8086, or NEC V20/V30, or 7.16MHz, etc.). So yes, with caveats.


I would think it work on those Tandys (EX, HX, SX) that allow you to change the speed by pressing the F4 key at startup if you did so.


3. Same color and black and white displayed colors as CGA: YES for the red/green/yellow and cyan/magenta/white palette with all background colors and intensities. I have *NOT* tested -- or do not remember if I have tested -- custom colors in 640x200, or the cyan/red/white palette. Due to the nature of how cyan/red/white is turned on, I would highly doubt it works.

BTW, it is interesting to note that the answer to #3 above (same colors as CGA) is NO for original IBM CGA. When I was testing 8088 Corruption, I was surprised to discover that 40x25 textmode has slightly different colors than expected (I don't mean everything was off by a hue, I mean that some colors were exact and others were quite different).

To show cyan/red/white on a real CGA, the color burst bit has to be off. It is Mode 5, which is B&W. If Mode 5 appears in B&W, then the question has been answered. Unfortunately, in order to fully test the 640x200 mode, you would have to cycle between all 15 valid color combinations (everything against black background.)

Interestingly, the Tandy should be even more flexible at composite than the CGA. The Tandy emulates the CGA, setting the PCjr. palette registers to the right colors. If you changed the colors in the palette, you would get many more possibilities.