SN65HVD1781A-Q1: Inquiry about setting DE, RE pins of SN65HVD1781A-Q1

Hi Do-Hyun,

You technically can do this. I usually recommend placing a pull up resistor on the R pin since the receiver being disabled will place the R pin into a high-Z state. I also suggest adding a pull up resistor on the D pin incase the TX line is ever high-Z.

I also recommend keeping the A/B lines of the device with lower capacitance to avoid any potential glitching when toggling: https://www.ti.com/lit/an/slla660/slla660.pdf?ts=1741122486315&ref_url=https%253A%252F%252Fwww.google.com%252F

-Bobby

I already have a pull-up on the R pin.
This is the first time I've heard of putting a pull-up on the D pin. Is this a universal method? I haven't seen any guides that say to put a pull-up on the D pin.

You need a pull-up on a line only if the device that is driving this line might be inactive. When your microcontroller takes some time to power on and initialize its TX pin, then it might sense to add a pull-up.