This port is the general link assist status. It is input-only. When the link assist receives a byte, it sets bits in this port to reflect the condition.

Bit 6 - this is set if there is an error condition
Bit 5 - this is set if the link assist is ready
Bit 4 - this is set if there is a byte waiting in the link assist
Bit 3 - this is set if a second byte is received while the first byte still has not been read by the CPU (i.e. this bit can only be set after bit 4 has been)