Leftover bits in SPI communication (Waveforms)

[Simone]

Hi,

I am trying to setup a SPI communication between t wo devices. I am sniffing the communication with a digital discovery.

The problem is that sometimes I have a strange output. As you can see see in the attached picture, the output "Leftover bits ...." appears. What does this mean?

What does the number after "Leftover bits"  mean?

Any suggestions about how to solve this problem? I don't understand if it is a configuration problem of the master or something else.

Thanks in advance,

Simone

[JColvin]

Hi @Simone,

I wanted to let you know that you placed your question in the correct section of the Forum where the engineer most familiar with the WaveForms software will be able to see and respond to your question.

There is a different Forum thread that mentions these leftover bits that seems to indicate that the chip select active low isn't properly lining up with the data transfer, though I wasn't able to readily find that source of information explaining that further.

Thanks,
JColvin

[attila]

Hi @Simone

The SPI is configured for interpret 16 bits / word and it looks like it detects not multiple of this during a CS active cycle.
This could be caused by: grounding issue, crosstalk between wires or ringing on clock signal.
Use the Logic Analyzer to have more information.

 

[Simone]

On 3/24/2023 at 12:37 PM, attila said:

Hi @Simone

The SPI is configured for interpret 16 bits / word and it looks like it detects not multiple of this during a CS active cycle.
This could be caused by: grounding issue, crosstalk between wires or ringing on clock signal.
Use the Logic Analyzer to have more information.

 

Thanks! it worked, it was crosstalk