SPI last bit on every byte is high

[inakimartinez]

Hi!

We see that the last bit in every Byte transmission on MOSI is set to high. We are using the SPI with DMA

If I read the registers of the SPI after the configuration I get:

- MCR   0x883F0000
- TCR    0x00000000
- CTAR  0x3E050004
- CTAR  0x78000000
- SR       0x42000000

If we connect the oscilloscope to the SPI lines we see the next:

Blue -> SCK

Red -> MOSI

Green -> /CS

Yellow -> /RESET (device reset)

inakimartinez_1-1650465653649.png

If we zoom on the MOSI and SCK lines we see the issue. This 2 bytes that can be seen in the capture are 0x52 and 0x00. You can see how the last bit goes high in both bytes.

inakimartinez_0-1650465630036.png

Does anyone know why this could be happening?

Regards,

Iñaki

[PabloAvalos]

Hi @inakimartinez 

Thank you so much for using our community. I really appreciate it.

I would like to help you in a proper way, so do you think may you share with me which part number you are using for? And then, may you tell me which devices you are trying to communicate via SPI ? Because those last 2 bytes does not make a lot of sense to me, but I would like to have more info to gladly help you of course.

I will stay tuned to your answer, so please let me know if you have more questions.

Thank you.
Best Regards.
Pablo Avalos.

[inakimartinez]

Hi Pablo.

Thanks for your fast response and help.

We are using the k24 microcontroller with the MCP3913 ADC. Find the datasheets we are using in the attachments.

Regards,

Iñaki

[PabloAvalos]

Hi @inakimartinez 

It is my pleasure to help you.

After checking what you are using for, it is unclear to me why it is happening to you those events at the end on the SPI frame. My suggestion is to check that your ADC chip is well connected and works correctly with the SPI clock from the MK24. After that, please download our SDK examples for TWR-K24 and try to run an example of dspi_interrupt_b2b_transfer_master with your ADC chip connected properly, and see if everything is ok.

Hope this steps might be helpful for you. Please let me know if you have more questions.

Best Regards.
Pablo Avalos.

[inakimartinez]

We have tested with the MOSI line disconnected in the ADC and the we see the same behaviour.

We are able to communicate with the ADC the most of the times, but there are other times that the data we receive from it does not make sense.

Thanks for you help.

[PabloAvalos]

Hi @inakimartinez 

Thank you so much for your reply and thanks a lot for your patience.

So, do you think is there anything else I can help you with? Because if communication with ADC works perfectly most of the times, what do you think is happening when it does not works fine? I am running out of ideas what could be the problem there with that intermittency.

Please let me know if you have more questions, otherwise, please mark this answer as solution.

Thank you so much.
Best Regards.
Pablo Avalos.

[inakimartinez]

Thanks for all your help, but It seems that the error with the ADC is not related to the SPI communication. We thought that as we saw that extrange behaviour on the SPI.

Regards,

Iñaki