Varunme, this thread is 5 years old. But to answer your question.
Full duplex means a communication link that goes in both directions at the same time, which requires two pairs of wires. The max485 is a transciever that alternately talks, then listens, on one pair of wires.
Yes, you could use four max485 chips, and have one of two at each hardwired as a transmitter and as a receiver.
But the max488 has a hardwired transmitter and receiver in one part, so it would do the same link with two parts instead of four.
Either way, you still need two wire pairs for full duplex.