A disassembly of CHRGET, left, and how it's been modified, $50 $f0 = bvc $73, which (infinitely) takes us back to The following value in memory, $f0, had been used as byte $50 This makes the next instruction bvc, clobbering for one phase and colorful for another phase. Sta $d020 Set the border color with whatever's in the org $007e Note that CHRGET itself begins at $0073. word $007e Wedge the code into CHRGET on the zero page. restore normal function, it's necessary to power-cycle RETURN is pressed the demo will just start again. RUN STOP - RESTORE will stop the program, but as soon as Holding down a key while this runs will produce an extra This demo loops about every 1.45 seconds (on an NTSC You can download the demo, NONMONOCHROME.įor my several readers who enjoy reading 6502 assembly, here’s what I did: Some extensive trickery was involved in injecting my code into existing memory contents to produce this effect. It’s also a bit more eye watering and more likely to trigger seizures.) While it’s a very simple effect, I don’t know of any demo at all for this platform that has this file size or any smaller one. (You can just as easily make the screen pulse, which I personally find less aesthetically pleasing because the pulsing in that case happens over any text that is on the screen. The effect is a pulsing pattern on the border. I contrived this one so that the 4b of code ends up overwriting part of a zero-page routine that runs every time RETURN is pressed. If you thought my last post about a 32 byte (plus 2 byte load address) Commodore 64 demo was esoteric, wait until you burrow into this one.īack in March at Lovebyte I released a C64 demo that is a total of 6 bytes.
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