Looking how RS-485 TX Enable PIN of XBee module is used. I suppose it’s active when a data to be transmitted (from module to serial). So one would use it as signal to enable 3-state RS485 driver and implement multi slave RS485 architecture to support REQUEST(originated from RS485)-RESPONSE(from wireless). XBee RS-485 Adapter datasheet does not provides any glue too.
Key question when TX-Enable signal is active.
Thanks