Protocol Analyzer -& SPI

[Ashwin10]

Hi, 

I am using protocol analyzer to monitor a SPI bus..

I have a STM32MCU used as SPI master, configured to run full duplex communication. There is no slave connected and I am just trying to understand the protocol itself.

It is configured the following way: CPHA = 0, CPOL = 0

I have plugged the 1st Probe(Orange) to the CLK and 2nd Probe(Blue) to the MOSI pins and I record the waveform, Parallelly I have made the following connections to the digital inputs to record them on the Protocol analyzer

DI 1(Green Wire) -> CLK

DI 2(Purple Wire) -> MOSI 

The purpose of this connection is to monitor the CLK and DATA out from the SPI using Scope and Protocol analyzer. 

The logic I have written in the STM32MCU is to send a value "0x1" out via SPI pin whenever a push button is pressed.

Below is the image of the data out from SPI that is captured in scope, the data out from the MCU is correct, every time I press the push button(SW delay is provided to prevent debouncing)

 

 

However I observe a different pattern while Spying the bus using protocol analyzer. I see the data being shifted every time I press the button(Image Below). You can see that the "11" values are being shifted every time I press the push button. The data transmitted is wrong (It sends "11" instead of 1)

 

My question is, if the data is shifted in the protocol analyzer window why bit shifting does not show on the scope?

 

 

[attila]

Hi @Ashwin10

It looks like the CS is not connected so the slave/spy can be out of sync and it does not show the bit-word grouping correctly.
See the CS/CLK/MOSI/(MISO) signals in the Logic Analyzer.