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STM32F427 SPI problem

Question asked by rubow.keith on Jun 25, 2015
I have observed a problem with the SPI port on my STM32F427 processor. If I set the speed of the output pin driving the SPI clock signal to LOW, the processor does not read the received SPI data correctly. The STM32F427 SPI port is in master mode. The SPI clock rate is about 1.3 MHz. I can observe correct received data with an oscilloscope. But the received data register is giving incorrect data. Note that I am referring to setting the output pin rise/fall time speed using the OSPEEDR register. If the clock output pin speed is set to FAST, everything works perfectly. If the clock output pin speed is set to LOW, incorrect data is received. I can verify all rise/fall times and data setup/hold times on the oscilloscope. The timing is well within spec with both FAST and LOW clock pin rise/fall speed settings. But with the LOW speed setting I can output SPI data to an external device just fine (device is a real time clock chip), but I get incorrect data when I READ the RTC.

Has anyone else seen a problem with the SPI clock pin speed set to LOW? I wanted a slower rise/fall time on the clock to eliminate some ringing on the SPI clock signal. But now I can't read the RTC!