NSS stays low after disabling SPI

[denisb-popov]

Posted on December 09, 2015 at 16:00

MCU: stm32f103rf

SPI: SPI1 without remap, MSTR = 1

SPI1 NSS pin PA4 configured as AF push-pull

PA4 remains low independent of SPI state (SPE, SSOE). When PA4 configured as GPIO it is working fine.

When running the same code with remaped SPI1 (also remap to SWD), NSS pin(PA15) goes high after it's configuration and enabling SPI1 clock (in any order).

Then it goes low after {SSOE = 1;  SPE =1}. Then it goes high after SPE = 0.