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Problem with stm32F446 output on pa6 and pa7

Question asked by Simon Andersen on Jan 22, 2018
Latest reply on Jan 23, 2018 by waclawek.jan

Hi, I've made a pcb using the stm32F446 mcu, 64 pin package, but I have a problem with it. I have four LED's attached to pa4 to pa7. Two of these work fine, but the ones on pa6 and pa7 only lights up entirely when both are on. I tried to remove everything attached to the pins, and saw on an oscilloscope how the output isn't the supposed 3.3v, unless both are on.

 

Oscilloscope probe

From here, you can see four stages: {both off},{ pa6 on, pa7 off}, { both on},{ pa6 off, pa7 on}. The probe is only measuring pa6.

 

Furthermore, when programming the chip using VisualGDB and stlink, sometimes it does not go to the programmed area after. When it doesn't, it goes there after a restart. And when it goes into this, pa6 and pa7 are both high. This is not much of a problem, but they might be correlated. I've noticed that the boot pin is floating, as it wasn't needed for the design, could this be causing the problems?

 

Thank you for any help

Simon

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