# unbrick switch on custom add-on board

Source: https://forum.modalai.com/topic/5400/unbrick-switch-on-custom-add-on-board
Category: Design Reviews and 3D Models (https://forum.modalai.com/category/39/design-reviews-and-3d-models)
Tags: system-review
Posted: 2026-08-28 13:36:43 UTC by Gerhold Ten Voorde
Replies: 1 · Views: 110

## Gerhold Ten Voorde · 2026-08-28 13:36:43 UTC

Hi,
We made our own add-on board for Voxl2. Now we want to add a switch, similar to SW2 on the Voxl2, to unbrick the board if needed.
I have seen that we can do it through pin 56 of connector J3. My questions: 

* list itemis this pin high active or low active? 

* list itemAre there resistors needed (like pull-up, pull-down, or in serie)? 

* list itemIf it is high-active, should I use pin 47 of J3?

Thanks

## Reply by Vinny (ModalAI staff) · 2026-08-31 17:15:23 UTC

Hi @gerhold-ten-voorde 
Yes, you are correct. Pin 56 is the signal "FORCE_USB_BOOT". It is default weakly pulled down by the SoC.
To enter eDL/QDL mode, this switch connects a 2-2.2K pullup to VREG_S4A_1P8 (J3 pin 47).
So, on M0154, the default OPEN/OFF position does noting, when ON it enables the pullup.
Hope that helps.
Thanks!
Vinny