[General] Unused RS-485 REciever inputs - PU or PD?

[Rocky&Bulwinkle]

I am working with an SP490E - RS-485 driver/receiver. I am looking for feedback on what to do with the unused Receiver Inputs, do I tie them high or low? The data sheet states the recievers are equipped with a "fail-safe" guaranteeing a high state if left unconnected. This PCB is not cramped for space so PU's would not be a problem. any recommendations from the design community?

Data Sheet:
The receivers for both the SP490E and SP491E have differential inputs with an input sensitivity as low as ±200mV. Input impedance of the receivers is typically 15kΩ (12kΩ minimum). A wide common mode range of -7V to +12V allows for large ground potential differences between systems. The receivers for both the SP490E and SP491E are equipped with the
fail-safe feature. Fail-safe guarantees that
the receiver output will be in a high state when the input is left unconnected.

 

[Gorgon]

If you are designing for production you should be aware that all compatible variants of this receiver is not reverting to high state if unconnected. I normally use pullup and pulldown resistors on all inputs to define the polarity when the receiver is floating/idle. We normally use 1k resistors, this will give you 300mV input signal when terminating with 120 ohm, at 5V supply.

This undefined polarity may give you a problem when switching direction on the RS485, in half duplex mode. If the input is unused, the pullup/down resistors does not draw any extra current with no 120 ohm termination.