<br>
== I/O Port Allocation Rules == {| class="wikitable"! rowspan=2|Hardware device !! rowspan=2|Read/Write !! colspan=16|Port bits|-! b15 !! b14 !! b13 !! b12 !! b11 !! b10 !! b9 !! b8 !! b7 !! b6 !! b5 !! b4 !! b3 !! b2 !! b1 !! b0|-| Gate-Array || Write Only || 0 || 1 || - || - || - || - || - || - || - || - || - || - || - || - || - || -|-| RAM Configuration || Write Only || 0 || - || - || - || - || - || - || - || - || - || - || - || - || - || - || -|-| CRTC || Read/Write || - || 0 || - || - || - || - || r1 || r0 || - || - || - || - || - || - || - || -|-| ROM select || Write only || - || - || 0 || - || - || - || - || - || - || - || - || - || - || - || - || -|-| Printer port || Write only || - || - || - || 0 || - || - || - || - || - || - || - || - || - || - || - || -|-| 8255 PPI || Read/Write || - || - || - || - || 0 || - || r1 || r0 || - || - || - || - || - || - || - || -|-| Expansion Peripherals || Read/Write || - || - || - || - || - || 0 || x || x || x || x || x || x || x || x || x || x|} Legend:*"-" means this bit is ignored,*"0" means the bit must be set to "0" for the hardware device to respond,*"1" means the bit must be set to "1" for the hardware device to respond.*"r1" and "r0" mean a bit used to define a register <br> == Official I/O Ports == The official ports are defined to eliminate conflict between devices, as follows:
{| class="wikitable"