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DP83848K: About Reset function

toshi-e2e
Genius 4760 points
Part Number: DP83848K

Hi all,
I have some questions about Reset function as follows;

Q1.While the H/W or S/W Reset is ON, I think the LED output will be OFF. For example, when RESET is executed, what is the delay time from the output low state to the LED output turning off?

Q2.If the voltage level of the strap is higher than 2V of VIH (min) of LED_Link at the time Reset is released, will that strap level be taken in as High?

Q3.Regarding the duration of the H/W Reset pulse, how long should Reset be low, especially when using only the internal pull-up resistor to set the Strap that is used together with the output, such as LED_LINK and LED_SPEED? 

Q4. After power-on, is it necessary to use S/W Reset together with H/W Reset? Is H/W Reset alone sufficient?

Q5. When I want to set the high level by the internal pull-up of the LED_LINK and LED_SPEED straps under the condition that there is no external pull-up strap, the method to ensure and accelerate these settings is LED Direct Control Register (LEDCR), address Is it effective to execute S/W Reset after writing "1" to 0x18 [5:4] and [2:1] to force the LED output to High?
The polarity of the LED is designed to be Low active.

Thanks and Regads,
Toshi

  • 0
    TI__Mastermind 31985 points

    Hello Toshi,

    1) We do not have this information.
    2) Yes, so long as it is like this during strap latch time.

    3) 1us as per section 5.6 of datasheet.

    4) Why would you need to use SW and HW reset after power-on? Do you mean in general if you need to reset the PHY during active operation? Either is sufficient. Please note that strapping will not re-latch on SW reset, but will for HW reset.

    5) Polarity is dependent on the strap of the LED pins. Will be active low if strapped high. Will be active high if strapped low. PHY should automatically take care of polarity upon strapping such that there is not need for further configuration; just make sure your schematic agrees with the convention.

    Sincerely,

    Gerome

  • 0 in reply to Gerome Cacho
    Genius 4760 points

    Hi Gerome-san,

    Thank you for your response and support.
    I understand about Q1 to Q3.

    Regarding Q4, 
    after the PHY is linked up after the H/W Reset, the MAC initialization program incorporates the S/W Reset execution program, so I thought that this process might not be necessary.

    I received a reply saying "Please note that strapping will not re-latch on SW reset, but will for HW reset.", but the section 6.4.6.2 Software Reset on page 37 of the data sheet has the following description, like H/W Reset, Strap information is reset.
    Is this datasheet wrong?
    --------------------Excerpt from the data sheet--------------
    The software reset will reset the device such that all registers will be reinitialized to default values and the hardware configuration values will be re-latched into the device.
    ------------------------------------------------------------------------

    Regarding Q5,
    If PHY's S/W Reset and H/W Reset are the same operation, I would like to discuss the following cases.

    In this particular PHY, the AN_0 (LED_LINK) information was originally supposed to be set as Strap information with the same High level information as the Internal Pull-up. However, after executing S/W Reset, a phenomenon occurred where it was judged to be low level and incorrect information was written to the register.

    Observing the waveform of AN_0, it is at the Low level because it is in the Link-up state before executing the S/W Reset.
    When the S/W Reset was executed, the voltage level of AN_0 (LED_LINK) only rose to about 1.5V within the period during which the internal RESET would have been executed (1 us in the specification, about 2 us in the observed waveform).
    I think that the internal pull-up resistance value may vary greatly, and it is presumed that this is the result of synergistic effects such as the capacitance of the LED itself.

    If the potential of AN_0 (LED_LINK) is raised to the same potential as the Internal Strap before executing S/W Reset, I think that there is almost no need to charge to raise it from 0V to Vcc via the internal pull-up resistor. .

    As a result, I thought that the strap information might be read as High level when executing S/W Reset, so I asked this question.

    As a way to set the LED_LINK and LED_SPEED pins to high level
    LEDCR register: 0x18 [5:4] and [2:1] are set to “1”.
    This method may differ from the original behavior of the PHY, but I thought of it as an emergency evacuation method. What do you think?

    Thanks and regards,
    Toshi

  • 0 in reply to toshi-e2e
    TI__Mastermind 31985 points

    Hi Toshi-san,

    You make a good point. I will need to check in with the team on this, but unfortunately, it will take a couple days due to US holiday on 5/29/23. I hope to give a response by 5/30/23 at latest.

    Sincerely,

    Gerome

  • +1 in reply to Gerome Cacho
    TI__Mastermind 31985 points

    Toshi-san,

    Perhaps it is as stated in the datasheet, and this relationship is not present in our current PHYs. Regarding the contingency you proposed, this does make sense to overwrite the LED control register.

    Sincerely,

    Gerome