RS485 on Real6410

I am trying to use the RS485 port on the Real6410 board.  I assume this is
device ttySAC3.  I can read from this port just fine but I can't write
anything.  Anybody know what is going on here?

I guess my question is "Does the driver that ships with the Real6410 board
have the ability to automatically toggle the pin that controls the RS485
transmitter?"

If so, how do I configure the port to do this?
If it doesn't, how do I control this pin?

Real6510 is a clone of the FriendlyARM designs? If it is the usual Samsung
reference design, the UART does not have CTS/RTS enables during standard
serial, only in MODEM mode (Unfortunately it is the way Samsung UARTs are
made). You need to have a driver that uses a GPIO pin to turn RS485 on/off,
or check the schematic and see if there is a direction detect circuit on
485 chip's direction lines that sniffs the Tx line from the UART.

These devices aplenty fast to do direction control in your code by directly
manipulating a GPIO pin to control direction. Just have a simple function
to turn transmit on or off. Turn it on, send data, turn it off and listen.
Even with an app written in Python under Debian on a 2440 you can do it in
a few microseconds.