The following table lists the main I/O definitions of the Studio IV.
|Q||Sound on/off, frequency as defined by tone latch|
|EF3||Key pressed on selected port (key pad 1)|
|EF4||Key pressed on selected port (key pad 2)|
|OUT 1||Tone latch, which sets tone frequency|
|OUT 2||Select key / port|
|OUT 4||bit 0-2 background colour, bit 3 white foreground, bit 4-5 enable graphics, bit 6 PAL/NTSC|
|OUT 5||Signal video chip to enable DMA towards the 1802 to fetch display data|