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Original question:

TCAN4550: SPI support CPOL=0; CPHA=1

TCAN4550: Evaluation module: issue with spi

Marco Semenzato
Prodigy 50 points
Part Number: TCAN4550


Hi,

I have an evaluation board of TCAN4550 FD. My problem is that TCAN4550 seems  not answering to the commands.

For test purposes I'm sending 0x41 (read command) 0x00 0x00 (address) 0x01(1 word to be read) following a dummy word 0xFFFFFFFF that should allow TCAN to answer.

Address 0000 should contain the datas 'T' 'C' 'A' 'N'

Attached are the screens of the command issued in the pin n#5 of TCAN4550 (pin n#14 of the eval board's J16 connector ) and the drive of CS (pin #18 of the eval board's J16 connector)

Image 1.jpg contains the CLK vs the MasterOutSlaveInput (pin n#14 of J16) 

Image 2.jpg contains CLK vs the CS (pin 18 of j16)

Image3 simp4ly shows that the bit is clocked out at the rising edge of the clock 

I performed the same test trying to set dummy byte to 0x000000 instead of 0xFFFFFFFF but nothing happened.

The pin 16 of j16 stays fixed low during all the duration of spi transmit.

I also tried to press the reset button and the wake button but no changes.

VIO select jumper is selecting 3.3 (so compatible with my SPI master)

All the other pins (except for SDI SDO SCLK and CS) are not used in the board and are floating.

Can anybody help me solve the issue?

Thanks

  • 0
    TI__Mastermind 34800 points

    Hi Marco,

    It appears that your clock polarity is incorrect and the data should be clocked out on the falling edge.  I am providing a complete logic analyzer plot I took of a successful read of register 0x0000 for your reference.  I have also pointed out the clock to data disparity between your plots and mine.  Correcting the clock polarity should resolve the issue.

    Regards,

    Jonathan

  • 0 in reply to Jonathan Nerger
    Prodigy 50 points

    Hi Jonathan,

    you're perfectly right. I tried to flip the polarity and now I can read corretcly.

    I was pretty sure I was using 0 0 mode. TCAN is compatible to 0 0? I'm asking to understand where I was wrong Slight smile

    By the way, thanks a lot. This thing spent me a lot of time.

    Regards,

    Marco.

  • +1 in reply to Marco Semenzato
    TI__Mastermind 34800 points

    Hi Marco,

    I'm glad I could help, and quickly identify the issue.  Yes, the TCAN4550 and TCAN4550-Q1 use SPI Mode 0.  It is in the datasheet as part of the "SPI Clocking" figure, but it is easy to miss.

    I hope you didn't spend too much time on this.  Feel free to reach out again if you have any additional questions.

    Regards,

    Jonathan