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TMS320F28388D: Some issues about PHY Reset Signal

Cherry Zhou
Mastermind 22235 points
Part Number: TMS320F28388D
Other Parts Discussed in Thread: TMDSCNCD28388D, DP83822I

Hi team,

Here're some issues from the customer may need your help:

1) As above description of PHY Reset Signal, here's 2 ways, one is the ESC and PHY synchronous reset, in which case the reset signal needs to be pulled down. Another mode is to release ESC and then PHY. In this way, the reset signal is the control of the IO and is controlled by the MCU. Is this correct?

2) When will the two reset modes be used? What are their prerequisites?

3) The following figure is the design in TMDSCNCD28388D, will GPIO155 require pulldown? 

 

Could you help check this case? Thanks.

Best Regards,

Cherry

  • 0
    TI__Guru 50611 points

    Cherry,

    The subject matter expert was out of office today. He will get back to you by tomorrow.

  • 0 in reply to Santosh Jha
    TI__Mastermind 45606 points

    Hi Cherry,

    Sorry for the delay. There were some previous confusions with the post assignment.

    Cherry Zhou said:
    1) As above description of PHY Reset Signal, here's 2 ways, one is the ESC and PHY synchronous reset, in which case the reset signal needs to be pulled down. Another mode is to release ESC and then PHY. In this way, the reset signal is the control of the IO and is controlled by the MCU. Is this correct?

    This is correct. In the first case the ESC_PHY_RESETn signal output is controlled by the F2838x's ESC module.

    Cherry Zhou said:
    2) When will the two reset modes be used? What are their prerequisites?

    I think my prior post (https://e2e.ti.com/support/microcontrollers/c2000-microcontrollers-group/c2000/f/c2000-microcontrollers-forum/1019744/tms320f28388s-esc_phy_resetn-signal) may answer this, partially at least. The choice of the reset being ESC controlled or IO (manually) controlled will depend on the system / PHY requirements (i.e. whether there's a reason to hold the PHY in reset longer or a need to manually control the PHY Reset signal rather than F2838x ESC).

    Cherry Zhou said:
    3) The following figure is the design in TMDSCNCD28388D, will GPIO155 require pulldown? 

    This is a good question and I'll need to review further. We document that a pull-down resistor should be used for ESC controlled reset, but maybe the ControlCARD design assumes reset is IO controlled.

    Also, I noticed that the RESET signal of the DP83822I is documented as having an internal pull-up on the signal.

    Best,

    Kevin

  • 0 in reply to Kevin Allen18
    TI__Mastermind 45606 points

    Hi Cherry,

    We think it's a good idea to put the pull-down resistor on GPIO155 (or whatever is used for PHY Reset).

    It's a good idea to implement it with an external pull-down to ensure that the default state of the PHY is disabled and is intentionally brought out of reset by the C2000 after power up. This is really only a concern when GPIO155 is in input mode however and once GPIO155 is switched to output mode (i.e. configured as a regular output or ESC_PHY_RESETn) then the signal will be driven by the c2000 in some way.

    Best,

    Kevin