Commodore VIC-20 PETSCII on the CoCo

In case you ever wondered what the VIC-20 character set would like like on a CoCo 1…

VIC-20 PETSCII (Uppercase 0-511) on a CoCo
VIC-20 PETSCII (Lowercase 0-511) on a CoCo

It would look like that.

And if you wanted to know what the VIC-20’s 22×23 screen would look like on a CoCo…

VIC-20 20×32 screen displaying PETSCII on a CoCo

That. It would look like that.

When I moved from the VIC-20 to the CoCo, I lost colors and sound, but gained a “huge” screen that was 32 columns wide instead of 22. But I lost horizontal lines (23 down to 16). It felt more usable (wider screen) but smaller.

It wasn’t until I started revisiting the VIC-20 this past year that I realized since each screen block was eight bytes tall, the VIC’s native “resolution” for that 22×23 screen would be 176×184 (22*8 by 23*8). The CoCo’s 256×192 was larger and could fit the VIC-20 screen with room to space (but without the colors).

When I tried to do a quick port of my VIC Sky-Ape-Er game, the different text resolution (22×23 versus 32×16) made all my levels need to be redesigned. It would not be the same game — but the same game engine with different sized levels that resembled the original.

It might be fun to come up with an assembly routine to handle VIC-20 custom characters on a 256×192 graphics screen. It would likely be slower (blitting out 8 bytes instead of printing one byte) than text mode, but I could then port my games over (minus color and sound) much more accurately.

Maybe some day…

4 thoughts on “Commodore VIC-20 PETSCII on the CoCo

  1. RogelioP

    Back in the day (when the stores displayed VIC-20s and Atari 400s on their floors), it was precisely the text screen of the VIC-20 that kept me away from it. In contrast, the still limited CoCo text screen seemed cleaner, well organized. Soon as I gathered knowledge about microprocessors (the 6800 being taught in Jr College) I went on full throttle with the CoCo.

    Today I own a VIC-20, love the little bugger – its cramped (but colorful) display actually part of its charm and personality :-)

    1. Allen Huffman Post author

      Remember all those high res screen programs for the CoCo 1/2? I want to make one that simulates the VIC-20 screen and PETSCII codes so I can port my old VIC stuff over.

      1. James D

        I have code that does 64 columns for the 6803, and some of the character generation code for the 6809. Wouldn’t be difficult to do 32 columns if I had the font data.

        1. Allen Huffman Post author

          The screen would need to be 22 x 23. I remember there used to be a hook in BASIC that let you send output to the printer or to a serial port or whatever. I expect these programs just made use of that. If they could look at the character to put it on the high resolution screen, then they could look at the character for escape codes and actually do cursor movements and all the other Commodore features.


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