Tandy Text Modes

[Great Hierophant]

Tandy 1000s have some unusual text modes. When connected to RGBI or monochrome/color composite monitors, the text is displayed in a 8x9 character cell, giving an effective resolution of 320x225 or 640x225. Normal PCs with CGA graphics use a 8x8 character cell, for 320x200 and 640x200 resolutions. However, if the output device is a TV via RF modulator, the Tandy uses an 8x8 character cell. This raises several important questions:

1. Can you safely run the Tandy 225-line modes on an ordinary CGA monitor like the 5153 or 4863, which expect 200-line modes?

2. Does putting the Tandy into TV mode, either using F2 at startup or through autoexec.bat, automatically turn off the color text?

3. If the answer to question two is yes, would it prevent the user or program from subsequently turning it on again?

 

[Trixter]

Tandy 1000s have some unusual text modes. When connected to RGBI or monochrome/color composite monitors, the text is displayed in a 8x9 character cell, giving an effective resolution of 320x225 or 640x225.

No, that's completely incorrect. It's 8x8 just like regular CGA.

 

[Great Hierophant]

No, that's completely incorrect. It's 8x8 just like regular CGA.

But the Tandy 1000 SX and TX manuals talk about of 640x225 and 8x9 text boxes when you use the F2 key, TV Mode/Monitor Mode. The values of the MC6845 are also slightly different from the PC's for those modes.

 

[Trixter]

I've never touched those. All I can tell you is that I own a Tandy 1000, 1000HD, and TL/2 and they all use 8x8.

Regardless of what "TV" mode does, I'm sure it will work on a regular monitor. There is a healthy dose of overscan that can handle overflow. (Or, you can program modes that dip into it -- I've successfully extended 80x25 textmode into 90x30 on CGA)

 

[vwestlife]

I've never touched those. All I can tell you is that I own a Tandy 1000, 1000HD, and TL/2 and they all use 8x8.

I have an original Tandy 1000 (with BIOS ROM version 01.00.00) and it uses 225-scan-line text mode by default. If you hit F12 during the startup memory check, it will boot up in 40-column, 200-scan-line text mode with the composite color burst enabled. Otherwise, you get 80-column, 225-scan-line text mode with the color burst disabled. You can also enter "MODE TV" (or "MODE 200") in Tandy DOS to switch to 200-scan-line text mode. "MODE 225" reverts back to 225-scan-line text mode. 225-scan-line text mode is viewable on the composite output, but it goes right to the edge of the screen, and might get cut off depending on the overscan adjustment on your monitor or TV set.

It's very easy to tell which mode you're using: type a lowercase "g" directly above an uppercase "T". If the descender of the "g" touches the top of the "T", you're using 200-line text mode. If there's a one-pixel gap between them, you're using 225-line text mode.

Beginning with the 1000SX, EX, and HX, Tandy used these function keys during startup:

F1 = Mono mode (disables color burst; otherwise the color burst is now turned on by default)
F2 = TV mode (same as F12 on an original 1000, as described above)
F3 = Swap floppy drive letter assignments
F4 = Slow mode (clock speed reduced to 4.77 MHz on an 8088 or 4 MHz on a 286) (or "MODE SLOW" in DOS, vs. "MODE FAST")

Edited for correct info.