This port is SE-only. On the TI-83 Plus Silver Edition, there is a hardware link assist. It frees the CPU from handling the link protocol by handling it itself, and interfacing through a set of ports.

Port 8 controls whether the link assist is enabled or disabled. You would want to disable it if you are directly controlling the link port through port 0, for example. Bits 0-6 are zero, and bit 7 sets whether it's enabled. If bit 7 is reset, then the link assist is active. If bit 7 is set, then it is disabled. (Counter-intuitive, I know).