Lab - 1: Modifications and Experiments

 

Modifications and Experiments

Changing color to Light Blue

To change the color, I replaced lda #$07 (yellow) with lda #$06 (light blue). The emulator provides a full-color reference table, making this an easy modification.

Different Color for each page

To add variety, I used different colors for each quarter of the screen:


Randomizing Pixel Colors

By integrating a pseudo-random number generator (PRNG) from the 6502 Emulator page, I assigned a random color to each pixel, creating a vibrant, chaotic display.

Advanced Experiments

Adding TYA Before STA ($40), Y


Effect

  • The screen will show a gradient instead of a single color.
  • Since TYA loads Y into A, the stored value changes as Y increments.
  • This results in 256 different colors across a page, depending on how the emulator maps colors.

Adding LSR after TYA


Effect

  • The screen still shows a gradient but with fewer unique colors.
  • LSR reduces the range of stored values, making colors repeat more frequently.
  • The total number of colors is reduced to 128, since LSR halves each value.
Using Multiple LSR Instructions

Try 2, 3, 4, or 5 LSR in a row.

Effect

  • With 3 LSR, the color range is now 32 unique colors.
  • More shifts (e.g., 5 LSR) would reduce to 8 colors or even fewer.
Using ASL Instead of LSR



Effect

  • ASL increases the brightness range instead of reducing it.
  • The values overflow quickly, creating sharp transitions between colors.
  • This can result in more rapid color changes compared to LSR.
Testing Multiple INY Instructions

Try replacing INY with two, three, or five consecutive INY commands.


Effect

  • The pattern becomes less detailed, as pixels get skipped.
  • 3 INY results in every third pixel being colored, creating vertical stripes.
  • 5 INY makes the gaps even larger.

We pushed the boundaries of our 6502 assembly knowledge, tweaking code, testing new instructions, and seeing the magic happen in real-time. But are you ready for a challenge? In the next post, we’ll take things up a notch with a tricky but fun assembly problem to solve. Think you can crack it? Let’s find out!

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