For the realization of an RS485 transceiver, I came across the question: How can bias, termination, signal filter and protection be best implemented in one design?
In my case, one RS485 master (with bias and termination, bus cable length < 2m, < 10 slaves, half duplex) and one RS485 slave should be implemented with the SN65HVD75 or similar integrated circuits.
RS485 Master with Bias and Termination
For a RS485 master transceiver with termination and bus bias, i found on my research implementations with a series resistor in each bus line - in front of the transceiver. These resistors (Rs) are used for current limiting during a transient event.
For adding bias and termination to this solution, i would place the resistors for bias and termination in front of the series resistors:
In an application report from TI, i also found this way - shown in a) (series resistors between termination and bias):
What is the right way to implement bus termination with bias using series resistors for current limiting during transient event?
Is the usage of series resistors in general a useful solution?
For filtering high frequency signal noise, can capacitors (1nF..10nF) be placed from each bus line to ground?
In other designs i researched solutions with a cm-chocke or series ferrits instead of series resistors:
What are the advantages of a design using series ferrites? What is a general good way to combine bias, termination, signal filtering and protection for a RS485 transceiver?