converting higher voltage data to 5vdc

[casdsys]

Hi all.
I have an application where data is being sent along 2 wires ( data/GND ) from a master device to a slave device.
The master device sends data out at between 5-20 volts dc to the slave, the slave converts it to a useable level of 5 volts dc.
Is there a method or component that will do this for me.

[pebe]

The easiest way would be to pass the data through a series resistor, with a 4.7V or 5.1V zener connected across the slave inputs.