• State
  • Locked Locked
  • Replies 5 replies
  • Subscribers 33 subscribers
  • Views 1162 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

DP83848I Link LED flashing @ 6Hz, Intermittent link.

JODY FELTHAM
Prodigy 40 points
Other Parts Discussed in Thread: DP83848I, ALP

Hi,

I'm using a DP83848I in-conjunction with the 9th MAC of a KSZ8999 switch. The DP83848I is the host port which connects to my LAN. The remaining 8 ports of the KSZ8999 are for system devices. I can sometimes ping a device which is plugged into any of the ports of the KSZ8999 but its very intermittent.   The LINK LED attached to the DP83848I is flashing continuously @ approximately 6Hz when a network cable is plugged into the port. The ACTIVITY LED is off.  Without a network cable attached the LINK LED is off. 

The DP83848I is configured as: LED MODE 2, MII MODE. RBIAS is 1.2V and the PFBOUT pins are 1.78V. The MDIO pin has a 2k2 pullup. 

What does the flashing of the LINK LED indicate? Has the PHY been configured incorrectly? 

The same LINK LED behaviour can be seen on all the prototype boards I have tried so its unlikely to be a faulty IC. I have even removed the KSZ8999 from the circuit and the same LED behaviour on the port connected to the DP83848I can be observed. 

Thanks for the help. 

  • 0
    TI__Mastermind 31600 points

    Jody,

    In LED Mode 2, the Link LED will blink at a 6Hz rate to indicate activity.  It sounds like what you are seeing is the correct functionality. 

    As a sanity check, you can manually configure the device to LED Mode 1 using the PHYCR[6:5] bits and confirm that the blinking stops.  The register address for PHYCR is 0x19.

    Patrick

  • 0 in reply to Patrick OFarrell
    Prodigy 40 points

    Patrick,

    Setting the LED MODE to 1 will certainly cause the LINK LED to stay on permanently with a network cable attached but why would there be activity periodically 6 times per second when there is no data on the the PHY's MII interface? 

    Jody. 

  • 0 in reply to JODY FELTHAM
    TI__Mastermind 31600 points

    Jody,

    Sorry, I interpreted the blinking as an indication of intentional packet traffic in one direction or the other. 

    Since the MII interface connects to the switch, could it be that the switch is transmitting packets without any action on your part?  What is connected to the PHY on the other side of the CAT-5 cable?  Could that PHY be transmitting occasionally?

    By probing the MII pins, you could possibly determine if there is packet traffic in the transmit or receive direction.  Probing the TX_EN, CRS, RX_DV, and RX_ER pins should give you some information. 

    Alternately, you could set the Isolate bit in the Basic Mode Control Register.  This will prevent packet traffic through the PHY MII pins.  If the source of the blinking is unintended transmit traffic from the switch, setting the Isolate bit should stop it.

    Patrick

  • 0 in reply to Patrick OFarrell
    Prodigy 40 points

    Patrick,

    The problem with the LINK LED flashing at 6Hz has been solved. There was a data line protection device between the isolation transformer and the RJ45. The protection device was not isolated from GND as specified in IEEE 802.3. When the device was isolated the LINK LED behaved as expected. 

    Unfortunately I'm still seeing a connection loss shortly after power up. On power up the PHY and Switch work for several seconds, long enough to get some data to transfer. After a few seconds the connection is then lost.

    I've been trying to diagnose the PHY using the Analog LaunchPAD utility V1.52. We have a demo board for a DP83849 which I can interrogate using the utility but as yet the utility can't detect the DP83848 on our design.

    Do you have any suggestions?

    Thanks.

    Jody. 

     

  • 0 in reply to JODY FELTHAM
    TI__Mastermind 31600 points

    Jody,

    Glad to hear you sorted out the problem with the link LED.  Nicely done.

    If you have ALP working with the DP83849, it should work with the DP83848.  My guess would be that there is some contention on the MDC / MDIO lines with the switch.  If so, is there a way to isolate the MDC / MDIO pins to the DP83848, with the 1.5 kOhm MDIO pull up resistor on the PHY side of the connection?

    Patrick