Video (PC8801)

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Port Name Function
0x30
0x34
0x35
0x52 Background Color Sets the background color of the screen. The color is an RGB composite.
If bit 3 (mask 0x8) = blue on
if bit 4 (mask 0x10) = green on
If bit 5 (mask 0x20) = red on
0x53
0x54 Toggle Background/Foreground color components Toggles background and foreground color components on and off
if 8-color mode {
  if bit 8 (mask 0x80) set, target is background color, else foreground
  if bit 7 (mask 0x40) toggle green component {
    GREEN ON if bits 1,2,3 (0x7) set, else OFF
  }
  else toggle red and/or blue {
    BLUE ON if bit 1,2,3 set, else OFF
    RED ON if value written / 8 sets bits 1,2,3, else OFF
  }
}
else if monochrome mode, set foreground color {
  BLUE ON if bit 1 set (mask 0x1)
  RED ON if bit 2 set (mask 0x2)
  GREEN ON if bit 3 set (mask 0x4)
}
0x55-0x5b Palette Write Writes to the palette. The index written to is the difference between the port number and 0x54.
if port 0x31 bit 6 (0x20) set {
  if bit 7 (mask 0x40) toggle green component {
    GREEN ON if bits 1,2,3 (0x7) set, else OFF
  }
  else toggle red and/or blue {
    BLUE ON if bit 1,2,3 set, else OFF
    RED ON if value written / 8 sets bits 1,2,3, else OFF
  }
}
else {
  BLUE ON if bit 1 set (mask 0x1)
  RED ON if bit 2 set (mask 0x2)
  GREEN ON if bit 3 set (mask 0x4)
}
0x5c-0x5f