Floating inputs on SN65HVD53DR

Hi Rohit,

If the receiver is enabled (/RE pin low), then the R output will be high whenever the differential input voltage (i.e., the voltage at the A pin minus the voltage at the B pin) is greater than VIT+, which is specified to be -20 mV (maximum). The R output would be low whenever the differential input voltage is below VIT-, which is specified to be -200 mV (minimum). In the case of a disconnected cable, you would typically expect a differential voltage close to 0 V as long as there are no other external circuits pulling the A or B signals up or down asymmetrically. So, in this case you would expect a high-level output from the R pin. If there is a large amount of differential noise present at the A/B terminals, though, there is a possibility of unintended toggling of the R output if the VIT- threshold is exceeded. This could be avoided by using a large-valued pull-up resistor on the A line and a large-valued pull-down resistor on the B line.

If the receiver is disabled (/RE pin high), then the R output will remain high impedance regardless of conditions on the A and B pins. Since you have this pin pulled up externally, the voltage on the R net would be high.

Let me know if you have any other questions.

Regards,
Max