The MAX13089E RS-485 transceiver can be used in either half or full-duplex mode. Connect H/F to VCC for half-duplex mode. Connect H/F to ground or leave it unconnected for full-duplex mode. There is an internal pull-down resistor for when the H/F pin is unconnected.
In half-duplex mode, Y and Z are the only active line driver/receiver terminals. A and B are internally terminated to ground. Y becomes the noninverting driver output and receiver input, Z becomes the inverting driver output and receiver input. A 120ohm resistor should be connected between Y and Z as close as possible to the pins. A and B can be left unconnected.
The figure below shows the internal connections of the MAX13089E in half-duplex mode.