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DP83869HM: DP83869HM NOT Switching in 100M / 1000M in media conversion application

guru sai
Intellectual 570 points

Part Number: DP83869HM
Other Parts Discussed in Thread: DP83869

Hi Sir,

We are using DP83869 For media conversion, copper to fiber. 

As per our application, we want to switch the Copper 100M mode to 1G mode. For this purpose, as per the earlier discussion with TI we are using JTAG_TDO/GPIO_1 (PIN 22) 

When JTAG_TDO/GPIO_1(pin 22) is connected to the SELECTION SWITCH as per the attached schematics

Our requirement: When the switch is high,  we should get 100 M operation; when the switch is low, we should get 1G operation.

Our strange observation: Whenever we connect the wire directly from the switch (PIN 1) OPMODE_0_BUF & OPMODE0 (Pin 22 : JTAG_TDO) then its working properly

But when buffer is placed in between OPMODE_0_BUF & OPMODE0 SIGNALS (AS PER THE SCHEMATICS) our system is in only 100M mode. not shifting to 1G mode even after toggling the switch.

How to resolve the issue?

Please support us

Regards

Guru

  • 0
    Intellectual 570 points

    Hi Sir,

    Please find the attached schematics

    .PDF-EPCB-2726-F-03_texas.pdf

    Regards

    Guru

  • 0 in reply to guru sai
    TI__Mastermind 36475 points

    Hi Guru,

    Can you measure the voltage at the JTAG_TDO pin while the PHY is resetting? So long as the voltage is within the specified range, you should see the operation mode change: 

    To confirm, you are placing the PHY in hardware reset when changing the mode correct? The PHY will not re-sample strap pins unless there is a power cycle or a reset.

    Best,

    Shane 

  • 0 in reply to Shane Hauser
    Intellectual 570 points

    Hi sir,

    As per the schematics, if we short U48 Pin 17 - Pin 3 with an external wire, the switching between 100M/1G mode is happening without any power cycle (switching we are doing via the SW3 Pin 1 &8)

    But without wire, with only the buffer its not switching

    Regards

    Guru

  • 0 in reply to guru sai
    TI__Mastermind 36475 points

    Hi Guru,

    The behavior you described suggests the buffer is interfering with the strap latch-in of OPMODE[0]. The most direct way to check this is by measuring the voltage value of the JTAG_TDO pin to see if it is expected.

    Another check you can perform is to read the strap latch-in register (0x006E[11:9]). What value do you see in this register in both the working and non-working cases? 

    guru sai said:
    the switching between 100M/1G mode is happening without any power cycle (switching we are doing via the SW3 Pin 1 &8)

    You are switching speeds without any power cycle or reset of the PHY? If you are changing strap modes, you should need a reset to re-read the straps.

    Best,

    Shane