Tandy Color Composite Output

[Cloudschatze]

I recently obtained a Tandy 1000 SX, and am finding that the colors in the composite output differ from those in the CGA screenshots found at MobyGames. Are Tandy and CGA composite modes not entirely compatible? Is it the (Commodore 1084) monitor I'm using?

[NewRisingSUn]

Known problem. Tandy onboard video has wrong artifact colors because the subcarrier phase is different.

If the monitor/TV set has a phase shift knob (labelled "tint" or "hue") with a large enough range, use it to compensate.

Just in case you're interested:
The subcarrier phase can be adjusted on a real IBM PC/XT by adjusting a trimpot labeled "COLOR ADJUST" on the main system board, as seen in IBM's "Technical Reference", page D-3. This adjusts the phase shift of the OSC signal on the ISA bus, which the CGA uses for its color subcarrier, whereas the pixel clock is based on the CLK signal from the ISA bus.

[Cloudschatze]

Thank-you for the info! I just finished reading through a chunk of the "40-Columns" thread on Vogons, where you've mentioned it as well. I did try adjusting the tint last night, but by fixing one color, another would then be off. I guess the adjustment range is the limiting factor here.

The Tandy has a potentiometer on its mainboard; I'll have to see what it does...

[NewRisingSUn]

fixing one color, another would then be off.

Is it a 640x200, or a 320x200-based game? Because adjusting the monitor only helps with 640x200 games.

320x200-based games can only be fixed with said trimpot (if it exists on the Tandy), because they mix artifact colors (which depend on the OSC signal phase, or more precisely: the OSC phase vs. the CLK phase) with solid colors (which don't depend on the OSC signal phase, as the CGA generates them in sync with OSC), requiring the proper phase difference between the OSC and CLK signals (315 degrees, if I recall correctly).

I just finished reading through a chunk of the "40-Columns" thread on Vogons

Don't. That monster of a thread is outdated and full of off-topic nonsense.

[Cloudschatze]

fixing one color, another would then be off.

Is it a 640x200, or a 320x200-based game? Because adjusting the monitor only helps with 640x200 games.

I'm not sure - it's whatever Ultima II uses. The "Ultima" text at the title screen is dark-green rather than blue.

[NewRisingSUn]

Ultima II is 320x200. No chance of just monitor-adjusting it.

[Cloudschatze]

I'm able to get it kind-of close with the tint adjustment.

[Great Hierophant]

Apparently you can run a real CGA card in a Tandy 1000 that has ISA-ish slots.  But I would think that any game that tried to read the status register of the CGA would also be reading the status register of the Tandy video hardware (which emulates CGA), which may not be in sync.  I don't see why you would want to though, because without the trimpot, it would show the same artifact colors as the Tandy video hardware.

[Cloudschatze]

Looking at the schematics, it doesn't appear that the Tandy trimpot has anything to do with the video. I'm not sure what it does yet. (Edit: It looks like might limit the speaker volume.)

The RGBI mode seems solid enough though.

Just as a side note, and unbeknownst to me when I bid, the system included a 20MB hardcard and 286-Express accelerator. Not bad for $1.99.

[BlueMax]

Ack!!   Lucky!!  What great addons!!!!

I'd love to have my beloved Tandy 1000SX back!

You aught to play games in Tandy graphics mode though - not CGA.  16 vs. 4 colours!

[NewRisingSUn]

I don't see why you would want to though, because without the trimpot, it would show the same artifact colors as the Tandy video hardware.

No. Strangely enough, using a CGA card in a Tandy computer produces correct colors, as seen in Servo's screenshots. Apparently, the OSC signal on the Tandy's ISA bus is correct, but the on-board video hardware doesn't use it.

[Great Hierophant]

In short, the Tandy 1000 SX is a sweet machine.  It is compatible with almost all games made for the IBM PC, runs at 4.77MHz or 9.44MHz, can run a true IBM CGA card with the proper composite colors, and is much more functional than a PCjr while retaining much of its compatibility.  Too bad the power supply doesn't supply a -5v line. 

[BlueMax]

Not to be nitpicky, but the SX's true speed is 50% faster than 4.77 = 7.155MHz.

Then again, you've got that 286 card in there doing interesting things!  Maaaan....  I would have loved one of those as a kid!

[Great Hierophant]

I know I had come across some computer in my travels that allowed a doubling of the clock speed from 4.77MHz to 9.44MHz, and if you use a 8088-10, the CPU could handle it.

I assume the PCjr displays the same artifact colors as the CGA card.

[Cloudschatze]

Hmm. Is the original IBM Color Graphics Adapter a full-length card? If so, it's about three inches too long to fit into an unmodified Tandy 1000 SX case...

[NewRisingSUn]

I don't know. Ask Servo about that.

[Great Hierophant]

Hmm. Is the original IBM Color Graphics Adapter a full-length card? If so, it's about three inches too long to fit into an unmodified Tandy 1000 SX case...

All the 8-bit IBM Video Adapters and the Hercules Graphics Card are full-length, without exception   I own one of each (except PGA and other unsuccessful products) and none would fit inside the covered machine. 

[Ari]

What about a TA-RA-RA-RA-BOOM-GA? 

[Cloudschatze]

Perhaps it's just the low-resolution monitor, but Zeliard looks *really* nice using the TGA option. Better than what I'm used to with either the EGA or MCGA settings and a VGA monitor.

Not only that, but as BlueMax has mentioned, the "four-channel" sound is pretty decent too, with the sound-effects being surprisingly good (compared to the same, as produced by the OPL-2/MT-32).

[glendower]

I really dug tandy graphics! All of my EGA friends were very jealous of the beautiful tandy colors on my 1000SL/2

Hmm... I didn't know that anyone actually *wanted* to see CGA colors correctly