SPI problem on STM32H7

[bacaneriaslocas]

Hello, I’m having a problem with a board I’m developing based on the STM32H747BIT6. The issue is related to SPI communication.

When I connect any device to the SPI bus, the signal level drops from 3.3 V to around 1.5 V. I have tested different SPI peripherals, but they all show the same behavior.

Could this be related to the drive strength or power capability of a specific pin?

[TDK]

Sounds like two pins are trying to drive the same line. How exactly are you connecting things? What things, what pins, what signal is dropping, etc?

[bacaneriaslocas]

 

This is the schematic of the sensor. My board was working fine until I had to replace the MCU due to a short circuit. After soldering the new MCU, the SPI signals driven by the M7 core are at around 1.5 V, while the SPI from the M4 core is working correctly.

The low voltage levels appear on SCK and MOSI. I’m assuming it’s a hardware issue, probably related to the power supply, but I haven’t been able to identify the source. The MCU pins seem to be correctly soldered.

I guess I just need to spend more time debugging, but I’m asking here in case someone has encountered a similar issue and can point out whether this is likely a power-related problem or something else.

[Andrew Neil]

Please show a complete schematic

How to write your question to maximize your chances to find a solution

 

Before getting into a custom design, have you tested this on a known-good ST board?

 

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@bacaneriaslocas wrote:

The low voltage levels appear on SCK and MOSI..

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If you just treat them as basic GPIO, can you set them high & low ?

[Chris21]

What happens if you remove the pull-up connected to the CS pin?