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IO / Functional Multiplexing during program execution

Lorenz Gruebler
Expert 1075 points

Other Parts Discussed in Thread: TMS570LS3137

Hello Forum,

 

CPU: TMS570LS3137

 

For HW Self Check reasons I want to switch the DCAN Interface TX Pin between GIO and functional mode during program execution. The RX terminal of the appropriate DCAN Controller need still to keep CAN RX functionality.

As I've found in the TRM (SPNU499, Tabe23-19 CAN TX IO Control Register Field Description) this function can be controlled by the Func field. There is mentioned that this bit is forced to 1 during initialization of the CAN controller.

Q: can I clear this bit to use I/O functionality during after the init of the can controller?

Q: is it possible to switch back to CAN mode without new initialization? (The HW Self check should be a short as possible!)

Q: Is there a similar possibility for the MII TX terminals?

 

regards,

 

Lorenz

 

  • 0
    TI__Intellectual 1325 points

    Hello Lorenz,

    We will look at this and back to you.

    Regards,

    Diwakar

  • 0
    TI__Intellectual 1325 points

    Hello Lorenz,

    Sorry for the delayed response.

    - MII does not support GIO functionality.

    - DCAN does support GIO mode, which can be used prior to DCAN initialization and DCAN node participating on the bus. But it is not recommended to switch back from functional to GIO mode once the DCAN communication is ongoing.

    Best regards,

    Diwakar

  • 0 in reply to Diwakar Bansal
    Expert 1075 points

    Follow up Question:

    Exists there a detailed description of each Signal Type of the Pins/Balls?

    Q: Still for self test purposes I want to set the DCAN TX Pin and the MII_TXD[n] Pins for a short period in hi-z mode. Is this possible?

    regards,

    logan54

  • 0 in reply to Lorenz Gruebler
    TI__Mastermind 20970 points

    Lorenz,

    the MII pins are not GIO configurable.

    The DCAN TX pin can be forced into a high Z state by configuring it as an input. This configuration is not recommended when the CAN is connected to the network (because the high-Z state is not a valid CAN TX state for the CAN protocol).

    Regards,

    Forum Support

  • 0 in reply to Kevin Lavery
    Expert 1075 points

    Hello Mr. Lavery,

    Is it possible to use GIO before set up the MII pins, because my Transceiver use Boot strap information after reset on MII_RXD, MII_RXER and MII_RXCLK.

    After set up the correct Bootstrap Information on the MII Pins by GIO Functionality, I will need to reset the PHY and switch the TMS570 to EMAC Mode.

    is this sequence possible?

    regards,

    Lorenz

  • 0 in reply to Lorenz Gruebler
    TI__Mastermind 20970 points

    Hi Lorenz!

    The balls of the 337 pin BGA are multiplexed, and the MII faimly of pins is not the default choice. That is, the balls are initially connected to other functionality that DOES have GIO capability. From the microcontroller's perspective, it is certainly possible to use the I/O capability of the default (or alternate muxing) pin selection and then change the ball to MII functionality.

    Whether the transition can be done in a way that works with the PHY is not assured, but the microcontroller can use the GIO functionality of the muxed pins and then change to MII (I'm not sure what kind of timing is required which is why "I don't know if the transition can be done in a way that works with the PHY"...).

    Best Regards,

    Kevin Lavery

  • 0 in reply to Kevin Lavery
    Expert 1075 points

    Thank you for your answer,

    I want to use the SMSC8710A, which requires bootstrap information. I'll take case about the reset and timing sequence. So it seems to be possible to use this PHY with HW-Bootstrap.

    regards,

    Lorenz