using RTS in multidrop RS485 application

I am trying to implement an RS485 serial interface. I have turned on the RTSTX in cont reg B and turned off RTS and RTSRX in cont reg A. I have set CDIR, CMODE and CSF bits for PORTC5. In this mode, I am expecting the RTS signal to go true only while characters are being sent out. Unfortunately, the RTS signal doesn’t change at all. What am I missing?