SPI signal looks weird on STM32F746

[RZahor]

Hi,

I have a custom board with STM32F746 MCU and XPT2046 touch controller (Clone of TI TSC2046E). They are connected on SPI2 (no other devices on this bus), running at ~210Kbit/s.

I couldn't get the touch controller to work correctly, so I've connected an oscilloscope to find that the signal itself looks pretty clean, but at the end of some bytes I can see a very long fall time (see attached pictures). Do I need to put pull-down resistors on the bus? I have never encountered this kind of problem with SPI before.

Any idea for solving this will be highly appreciated,

Thanks,

Roy

[TDK · Accepted solution]

SPI devices often put the MISO line into a high-z state after the transmission is complete. There's no problem with this as the value is don't care at that point.

[RZahor]

Thank you very much, I learned something new :)