RS485 topology, end resistors and baudrate for home automation.

Rs485 can be used effectively over long distances and in electrically noisy environments, using linear bus topology with two end resistors.

RS485 linear bus topology

However Mixed topology is easier to implement in a house (that is my case)

RS485 Mixed topology without end resistors

In this case we can't put a resistor in every end of the cable.
In order to prevent data corruption, propagation delay should be much smaller (15 times or more) than one bit width, then end resistor is no needed.

In other words, maximum  baudrate depends on cable length.
As a rule, for cable length up 200 metres safe speed is 28600 bps and for cable length up 600 metres safe speed is  9600 bps.

In My Automatic House (MAH), in spite of cable distance is less than 200 mts I'm using 9600 bps which is enough for regular use.


References
The RS-485 Design Guide (Rev. B - Texas Instruments)
RS485 & RS422 - When is termination required?
http://en.wikipedia.org/wiki/RS-485