# Ethernet Expansion & USB Hub: I2C Internal Pull-Up Resistors

Source: https://forum.modalai.com/topic/4999/ethernet-expansion-usb-hub-i2c-internal-pull-up-resistors
Category: General Questions (https://forum.modalai.com/category/2/general-questions)
Posted: 2026-01-21 01:02:28 UTC by shawn_ricardo
Replies: 3 · Views: 363

## shawn_ricardo · 2026-01-21 01:02:28 UTC

Hello,

I'd like to use J9 2W UART + I2C Port on the Ethernet Expansion & USB Hub.

Does this port include pull-up resistors? Is there a way to control resistance settings? Do you have recommendations/tutorials on how to use this specific I2C port? I have the circuitry / sensors working on bench using Arduino + RPI (I2C master). Trying to port this functionality to VOXL2 being the I2C master.

Thank you for any advice!

Shawn Ricardo

## Reply by shawn_ricardo · 2026-01-21 21:07:58 UTC

Without and without ethernet expansion hub connected, ls /dev/i2c-* shows the same output:

```
voxl2:/$ ll /dev/i2c*
crw-rw---- 1 root i2c 89, 0 Mar  2  2023 /dev/i2c-0
crw-rw---- 1 root i2c 89, 1 Mar  2  2023 /dev/i2c-1
crw-rw---- 1 root i2c 89, 2 Mar  2  2023 /dev/i2c-2
crw-rw---- 1 root i2c 89, 3 Mar  2  2023 /dev/i2c-3
crw-rw---- 1 root i2c 89, 4 Mar  2  2023 /dev/i2c-4
crw-rw---- 1 root i2c 89, 5 Mar  2  2023 /dev/i2c-5
```

Appears no new i2c interfaces are detected. Is there some software that needs to be configured / enabled?

Also noticed that no SPI interfaces are newly available:

```
voxl2:/$  ls /dev/i2c-*
/dev/i2c-0  /dev/i2c-1  /dev/i2c-2  /dev/i2c-3  /dev/i2c-4  /dev/i2c-5
```

## Reply by shawn_ricardo · 2026-01-21 21:44:57 UTC

For more context, I am only using SDA, SCL, and GND pins

![32367222-3f10-4f8b-bf0c-94778d8a3f9b-image.png](https://forum.modalai.com/assets/uploads/files/1769031855839-32367222-3f10-4f8b-bf0c-94778d8a3f9b-image.png) 

The MCU runs on 3.3 logic level voltage -- again, was able to work properly with a RPi5 I2C

## Reply by Vinny (ModalAI staff) · 2026-01-22 16:34:10 UTC (in reply to shawn_ricardo)

Hi @shawn_ricardo 
Yes, any I2C port on an expansion board has 2.2K pullups to the voltage on Pin 1 of that connector.

The Linux Kernel user guide has info on which QUPS are enabled or not in which system image. 
![3356687b-6e2d-4443-9a15-6e9aa07566d1-image.png](https://forum.modalai.com/assets/uploads/files/1769099579133-3356687b-6e2d-4443-9a15-6e9aa07566d1-image.png) 
 and specifically this helps:
https://docs.modalai.com/voxl2-qups/
Note not all QUPs have actually been enabled in the system, but with the sets of ports we have enabled, we never had any customer claim of a shortage: