Re: Enabling auto RS485 half-duplex control

[Theodore Tso <tytso@mit.edu>]

On Wed, Dec 17, 2008 at 10:24:13PM +0100, Matthias Fuchs wrote:
> Hi,
> 
> some Exar UARTs like the XR16C2850 support a feature
> called auto RS485 half-duplex control. In this mode the
> RTS line has a special role when using the UART for 
> RS485 communication.

So I haven't maintained the serial driver for a long time, but when I
did, I refused to try to implement hardware half-duplex control
because there was absolutely no standards in this space.  Which RS-232
lines are involved wasn't standardized, and there was often very
strange timing restrictions as well.  Some devices required there to
be a minimum delay of XX milliseconds between when RTS is raised
and when DTR is raised.  Other devices have a maximum time between
when one side raises RTS and the others side raises DTR.

So the challenge is designing an interface for half-duplex which is
sufficiently general that it will actually work for all/most of the
half-dozen people in the world who still care about half-ruplex RS-232
communications.  :-)

						- Ted