What Causes Partial Error Codes to Occur When the SPI Data Is Correct?

Question from the Customer:

I’m using the Beagle I2C/SPI Protocol Analyzer and the Data Center Software. I have a question about the results I see. I send a 20-bit (2.5bytes) data packet, and the results show the data is wrong.  The error code is P4, as shown below.

Viewing error codes in Data Center SoftwareWe are certain the SPI data is correct – why is the Data Center Software  showing an error?

Response from Technical Support:

Thanks for your question! The P4 (in the Error column in Data Center Software Transaction Log) indicates Partial last byte (P) errors.

What (P) Errors Indicate

Since the analyzer operates at a byte level, this error indicates the analyzer was not able to capture an entire byte. The number following the P (such as P4) represents how many bits of the last byte were captured.

Details About the Error Message P4

For SPI, the Beagle I2C/SPI analyzer uses the SPI slave select line to frame each transaction. The cause for this issue (P4) can be that the Beagle I2C/SPI analyzer sees 4 bits and the slave select line goes inactive, and then pads the rest of the byte with 0s.

For descriptions of all error codes, please refer to the Error Codes Table in section General Monitoring in the Data Center Software User Manual.

Sampling Rates Can Affect SPI Data Results

There are three different sampling rates that can be used to monitor the SPI bus. As a rule of thumb, it is recommended that the sampling rate be at least 4 times faster than the data rate of the monitored bus.

We hope this answers your questions. Additional resources that you may find helpful include the following:

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