Is UART1_RXD (Pin 10) 5V-tolerant?

Is UART1_RXD (Pin 10 on the Jetson Xavier NX carrier board) 5V-tolerant?

Let’s assume I have a 3rd-party transmit-only UART device that uses 5V TTL levels and is powered via +5V (Pin 2/4) and GND (Pin 6) on the NX carrier board.

Can I safely connect the device’s (5V TTL) TX pin to UART1_RXD (Pin 10) on the NX carrier board?

No, it is 1.8V pin.

I’m confused. My question was referring to the Jetson Xavier NX Developer Kit (SKU 945-83518-000x-000). Specifically, the included NVIDIA-designed reference carrier board, NOT the “naked” NVIDIA Jetson Xavier NX module (SKU 900-83668-0000-000).

Page 4 of the carrier board specifications [*] shows that there are level shifters present between UART#1 and the 40-pin expansion connector. Section 3.3 (page 21) of the specifications explicitly state: “All the signals on the Expansion Header use 3.3V levels.”

So why would it only accept 1.8V?

In my (admittedly limited) experience, it’s not completely unheard of for 3.3V inputs to be 5.0V-tolerant, hence my question.

[*] NVIDIA Jetson Xavier NX Developer Kit Carrier Board (P3509 A01) Specification

Yes, the module pin is 1.8V, there is a level shift to convert to 3.3V on devkit carrier board. 5V is not suggested to that.

Do you have the part number / datasheet of the level shifter?

You can find that in P3509 schematic/BOM in DLC. Jetson Download Center | NVIDIA Developer

The BOM doesn’t really help, since it lists at least four different level shifters and I’m unable to tell which one is which.

I eventually figured out that what I needed to look at were the circuit board schematics. They are part of the “Jetson Xavier NX Developer Kit Carrier Board Design Package (P3509 A01)”. The part I was looking for is a TXB0108RGYR 8-Bit Bidirectional Voltage-Level Shifter with Auto Direction Sensing and +/-15-kV ESD Protect.

The TXB0108’s datasheet specifies the absolute maximum input voltage range (V_I) on the B-port as +6.5V, so I figured it was safe to just wire everything up as described in my initial question and test it out. Turns out it works! (I can read data from /dev/ttyTHS0 with 115200 bps).

So, I guess the answer to my question is: Yes. (With a caveat that doing so would exceed the TXB0108’s recommended operating conditions, but not its absolute maximum ratings. I’m not experienced enough in electrical engineering to tell if there are any additional issues I haven’t considered.)