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TMDX570LC43HDK: Using 3-Wire SPI on Hercules

Danilo
Prodigy 10 points
Part Number: TMDX570LC43HDK

Tool/software:

Hi everyone,

I'm working with the TMDX570LC43HDK (Hercules) and I want to use the SPI interface in a 3-wire configuration. Specifically:

  • I’m not using the CS (Chip Select) line.
  • I plan to tie MISO and MOSI together using a 10kΩ resistor.
  • This combined line will be connected to a digital I/O pin.
  • I’ve seen that some devices support this kind of configuration, but I’m wondering: Is the Hercules (TMS570LC43x) SPI or MibSPI module compatible with this setup?

Thanks in advance.

Best regards,

Dani

  • 0
    TI__Guru 69891 points

    Hi Dani,

    Danilo said:
    • I plan to tie MISO and MOSI together using a 10kΩ resistor.
    • This combined line will be connected to a digital I/O pin.

    I don't see any issue in connecting these both lines together, because if we select SPI master configuration than MOSI will act as an output and MISO will act as an input right so i don't see any issue in shorting these two lines.

    And if we do this then i think we can just readback the data that we sent out of MOSI line through MISO line.

    I think whatever we write on SPIDATx register will also readback from SPIBUF, if this is your requirement then you can proceed to do it.

    --

    Thanks & regards,
    Jagadish.

  • 0 in reply to jagadish gundavarapu
    Prodigy 10 points

    Hello Jagadish,

    Thanks for your answer.

    In our case the Hercules will act as a slave, since the device we need to connect to will send information/diagnostics acting as a master so that the device will provide the clock. In this case, shorting MISO and MOSI is still not a problem?

    Thanks in advance

    Dani

  • 0 in reply to Danilo
    TI__Guru 69891 points

    Hi Dani,

    Danilo said:
    In our case the Hercules will act as a slave, since the device we need to connect to will send information/diagnostics acting as a master so that the device will provide the clock. In this case, shorting MISO and MOSI is still not a problem?

    In this case it might create problem if we directly shorted Slave out and Slave in lines of the controller.

    But as you said if we connect a series resistor to the slave out line that might prevent the issue:

    After connecting resistor, i don't think there will be any problems while receiving data from other end master, however if this device needs to send some data to other end device that might create problem because SPI is a full duplex communication right, that means master and salve will parallelly sends the data so if slave is transferring data then master also might transfer data this will conflict the communication if you short the lines.

    So do a prototype at your end to verify your requirements. And based on that you can proceed further.

    --
    Thanks & regards,

    Jagadish.