Pac-Man Joke

I thought it would be fun to have the TRS-80 Model III display the Pac-Man chart joke. If you have a Model III handy (with at least 16K), or access to a good emulator, you can download the program and run it for yourself. I've included both disk and cassette format executables.

Here's a picture if you don't have the equipment or can't be bothered.

The program synchronizes with the display refresh in order to eke out higher than normal vertical resolution. This means it won't work on a Model I or on a Model 4. However, it will work on any Model III, even those used outside North America whose screens refresh at 50 rather than 60 Hz. I also put in code to auto-detect the TRS-80 model number and display a message warning that things are not likely to work out.

I started out thinking I would write the display code by hand, but that became tedious rather quickly. Instead I drew the picture I wanted and wrote a program that processes that into the necessary screen writes with all the careful timing. It is somewhat akin to a compiler and like a compiler there are lots of pictures that would be possible to display but it would not generate working code for them. It also wastes quite a lot of space on timing as it mostly blasts out NOPs as needed. My apologies to those who load it from cassette.

I'd love to hear from you if it doesn't work on your Model III.

---

George Phillips, April 3, 2014. george -at- 48k.ca