NUCLEO‑N657X0‑Q: 0-Ohm Bridges in XSPI OCTOSPI Traces

JGiss.1 · ‎2025-10-09

I’m designing a custom board based on STM32N6 and using the same boot flash as the NUCLEO‑N657X0‑Q (MB1940). In the reference design, all OCTOSPI signals to the flash have 0‑Ω bridges in series, and the traces are length‑matched including those footprints.
What’s the main reason for these 0‑Ω parts? Are they only for flexibility during bring‑up (e.g., swapping in damping resistors), or do they serve another purpose? Is it safe to omit them or do they serve a specific reason?

Snippet from the MB1940 Schematic:

Thanks in advance and best regards,

Julius

Andrew Neil · ‎2025-10-09

@JGiss.1 wrote:
What’s the main reason for these 0‑Ω parts?

So that people who want to disconnect the memory (eg, to use the pins as GPIO) can easily do it.

Remember that Nucleos are intended as general purpose evaluation tools.

A complex system that works is invariably found to have evolved from a simple system that worked.
A complex system designed from scratch never works and cannot be patched up to make it work.

JGiss.1 · ‎2025-10-09

@Andrew Neil wrote:
So that people who want to disconnect the memory (eg, to use the pins as GPIO) can easily do it.

Thanks for your answer!

This would make a lot of sense to me if the pins were routed out on a connector, which they aren't. That's why I thought this would be an unlikely reason for the bridges. RMII/USB/... Pins all don't have any solderbrdiges in their traces to make them usable as GPIO or any other function.