Video (PC8801)

Port	Name	Function
0x30
0x34
0x35
0x52	Background Color	Sets the background color of the screen. The color is an RGB composite. BLUE ON if bit 3 (mask 0x8) set GREEN ON if bit 4 (mask 0x10) set RED ON if bit 5 (mask 0x20) set
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