>On the SE: All ports between 0-3Fh are either zero, or have some value. >Every port 40h-0FFh is set to 0FFh. Thus all usable ports must be in the >00-3Fh, though that's no gaurantee that *all* ports in this range are used). >0 - link (direct line access) Do you mean that linking like on the TI-83 (plus) *is* possible? i.e. out(00),C0 ?