How important is it to use a regulated supply for RS-485? I am planning on using an unregulated isolated DC-DC supply for a basic low-speed RS-485 circuit. The power supply noise would be greatest when the data line switches state, which could be mitigated by including a fair amount of decoupling capacitance on the supply. I plan on using a 100 to 120-Ohm termination resistor at each end. Since the data is asynchronous and the data rate is low, the switching noise shouldn't interfere with the data transmission since the data sampling point is in between the switching events. Am I losing very much noise margin by using an unregulated supply? At worst case, assume the supply could range from 5.5V at no load, to 4.7V at full load.
Thanks,
Greg