High-Res Graphics on a Text-Only TRS-80 Model 4 from 1983

http://www.bytecellar.com/2018/10/17/enjoying-high-res-graphics-on-a-text-only-trs-80-model-4-from-1983/

by blakespot • 8 years ago

69 17 8 years ago

XalvinX• 8 years ago

In about 1980 or so i got a TI 99/4A (I was about 12) and figured out how to do high-res graphics within the limitations of what was essentially a text-only machine. By redefining the 8x8 character blocks you could manipulate individual pixels. The main limitation was that when you redefined one character, every one of that number on the screen would change, and I think there were 256 available...still though, i managed to create programs that could graph a line and draw circles, and something that was similar to Missile Command. it was also interesting in that if, for example, you filled the whole screen with a single character and then redefined it in a loop or something, the whole screen would instantly update creating mesmerizing effects. You had to be creative in those days.

mmjaa3• 8 years ago

My favourite 8-bit machine, the Oric-1/Atmos range of systems, had a secret video mode embedded in its bowels that we didn't know much about until this century. It turns out there is a way to do color rendering on the Oric that precludes the attribute clash that inflicted so many systems of the era .. and we didn't find out about it until one of our most elite hackers dug deep.

Since then, there's been a re-birth of new titles written for the Oric to exploit this graphics mode .. and it has resulted in titles that, had they occurred in the 80's, would have propelled the Oric far further into the scene - perhaps. (Perhaps, it was already too late for the Oric by the time it arrived...)

I find it fascinating that these machines still hold so many treasures yet to discover. And, it sure is fun to be writing software for an 8-bit machine, with only perhaps a few hundred users out there who would give a damn ..

andrewstuart• 8 years ago

any references to this display mode? I can't find anything on it on the net.

tssva• 8 years ago

What you described is graphics mode 1 or standard graphics. The TI 99/4a also had a mode 2 or bitmap mode. In this mode the screen was divided into thirds each being assigned their own character pattern and color table. This allowed you to change each pixel on the screen individually.

There was still a color restriction. Each row of a character could only contain 2 colors, so every horizontal grouping of 8 pixels could only be one of two colors assigned to that row in the character. This is still an improvement over standard mode which required all pixels of an 8x8 pixel grid defined by a character to be one of two colors assigned to that character.

ams6110• 8 years ago

IIRC you needed the MiniMemory cartridge and the assembler program it came with (on cassette tape) to access this mode as a programmer.

blakespot• 8 years ago

I typed in many a BASIC program from '99er magazine, Family Computing, Compute!, and the like that used the mode you speak of, redefining characters to be shapes of the needed sort. This was used in the program I typed in for this blog post last year: http://www.bytecellar.com/2017/10/03/a-program-from-a-35-yea...

boomlinde• 8 years ago

A bit disappointed that this was just a matter of installing a graphics board in a machine designed to host one when it sounds like it would be a nifty hack from the title.

Still an interesting read to someone like me who knows very little about the Radio Shack computers.

torgoguys• 8 years ago

I had a lot of fun with a TRS80 Model 4D when I was a kid. The article actually has the "text mode graphics" resolution wrong. There were characters divided 2x3 blocks so you could divide the 80x24 character screen into 160x72 ”pixels” natively, without the extra hardware used in the article.

Since characters were simultaneously available at the full hi res of the screen, this allowed me to make a pretty nice looking rouguelike style game. Text heavy, but using the block pixels for walls and some limited graphics effects.

kbutler• 8 years ago

The Model III display was only 64 characters per line (64x16), so the 2x3 blocks gave you 128 horizontal "pixels". Model 4 could operate in either Model III (backward compatible) or Model 4 mode.

Moving to 80x24 on PC from a Model III was huge.

pohl• 8 years ago

This post made my childhood come rushing back. I was fortunate to grow up with a new-at-the-time Model I, which my father and I upgraded piecemeal from a Level I Basic ROM to the Level II ROM, then adding the expansion bay, filling it with 48K (16K at a time), then the chip that allowed displaying lowercase letters, and eventually 4 external double-density floppy drives.

The Model 4 was the machine that I would daydream about while flipping through Radio Shack catalogs and "80 Microcomputing" magazine. I was determined that, when I grew up, I'd have a Model 4 with both banks of RAM (128K total) and 4 internal half-height floppy drives in the bays (I don't think that was possible, in retrospect), and the hi-res card.

I still love the look of this machine.

potta_coffee2• 8 years ago

This was my first computer. Dad threw it away when I was at college, I was disappointed. Wish I still had it.

behringer2• 8 years ago

Come to Tandy Assembly next month in OH and relive your glory days.

potta_coffee2• 8 years ago

That would be awesome! I'm way far away from OH though.

High-Res Graphics on a Text-Only TRS-80 Model 4 from 1983

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