TI-H: asm

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TI-H: asm


ok...i am trying my best to learn how to program in assembly using
zshell...right now i am a little stuck though...will someone please explain to
me how and why these routines (from the zshell school) actually work (word for
word).

PLOTTING PIXELS

Here are four routines for putting a pixel, removing a pixel, changing a
pixel, and checking to see if a pixel is lit.

     PutPixel: ; Puts a pixel at B,C
      ROM_CALL(FIND_PIXEL)
      ld de,$FC00
      add hl,de
      or (hl)
      ld (hl),a
      ret

     RemovePixel: ; Removes a pixel at B,C
      ROM_CALL(FIND_PIXEL)
      ld de,$FC00
      add hl,de
      cpl
      and (hl)
      ld (hl),a
      ret

     ChangePixel: ; Changes the pixel at B,C
      ROM_CALL(FIND_PIXEL)
      ld de,$FC00
      add hl,de
      xor (hl)
      ld (hl),a
      ret

     TestPixel: ; Tests the pixel at B,C. If the Z flag is set, no pixel, else
a pixel is lit
      ROM_CALL(FIND_PIXEL)
      ld de,$FC00
      add hl,de
      and (hl)
      ret
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