AH = 0Ch: Write Graphics Pixel

This function writes a pixel on the screen in graphics video modes. If bit 7 of register AL is set, an exclusive OR (XOR) is performed on the current pixel value in display memory and the bit value given in bit 0 (or bits 0,1 if in low resolution graphics modes) of register AL. If bit 7 is clear, the specified pixel value REPLACES the current one at the given address. The range of valid pixel (x,y) addresses depends on the video mode.

• Input: AH = 0Ch
  AL = Pixel Color (bit 7 is XOR flag):
  Bit 7:
  If 1, XOR pixel with current value
  If 0, replace current value with pixel
  Bit 0: Pixel value if in hi-res graphics
  Bits 1,0: Pixel value if in lo-res graphics
  BH = Page (not used for HP 100LX)
  CX = x (Column or Horizontal pixel address)
  DX = y (Row or Vertical pixel address)
  

• Output: None
• Error conditions: None
• Registers modified: AX