XBee PRO S2B not working outside an explorer board

I have an 2 XBee PRO S2B modules, one of which acts as a co-ordinator and the other as a router. The problem is that when both these modules are on a USB explorer board, it works fine i.e. they communicate with each other properly and the co-ordinator recognizes the router properly with the ATND command.
When I connect the router directly to a 3.3 V supply, with DIN and DOUT connected to an RS-232 transceiver, the co-ordinator does not recognize the router and no communication takes place. I ties the Reset pin to Vcc without any success.

Do you have the XCS module? I don’t think the S2B (ZigBee) is related to this forum.

The manuals define the minimum number of pins to connect, plus the recommended pins. Are you sure the RS-232 pins are right? having 2 outputs linked (and 2 inputs) means it won’t talk. Also, their default ‘idle’ state should be high/3.3v