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LED Direct Control in DP83848

paddu1
Expert 1195 points
Other Parts Discussed in Thread: DP83848I

Hi,

The DP83848I datasheet mentions that
"DP83848I provides another option to directly control
any or all LED outputs through the LED Direct Control Register (LEDCR)"

Is it possible to control the LED outputs(ON OFF & Duty cycle) of LINK,ACT,SPEED
with this register? Is there any way to control the duty cycle also?

Regards
paddu

  • 0
    TI__Mastermind 31600 points

    Paddu,

    The LEDCR register allows the LEDs to be driven directly, but it only allows the LEDs to be driven high or low.  Consecutive writes to the LEDCR that alternate the LED(s) high or low would create a toggling waveform, but the duty cycle would be limited by the bandwidth of the MDC/MDIO register accesses. 

    What is your design goal in terms of the duty cycle?  What are you trying to implement with the LEDs?

    Patrick

  • 0 in reply to Patrick OFarrell
    Expert 1195 points

    Thank you Patrick,

    Regarding your question, there is no special design goal in terms of the duty cycle.

    As you know, LED light has a Lifespan and the LED's which we are using has
    little bit lesser lifespan,
    so we are thinking instead of keeping the LED's ON all the time,
    we can ON and OFF with a duty cycle and increase the Lifespan.

    Regards.
    Paddu.

  • 0 in reply to paddu1
    TI__Mastermind 31600 points

    Paddu,

    So using the LEDCR to toggle the LEDs on and off should meet your needs? 

    Patrick

  • 0 in reply to Patrick OFarrell
    Expert 1195 points

    Hi Patrick,

    As you wrote the duty cycle will be limited by the bandwidth of the
    MDC/MDIO register accesses.
    We are still evaluating whether this method increases the lifespan.

    Regards
    paddu

  • 0 in reply to paddu1
    Intellectual 840 points

    paddu1 said:

    Hi Patrick,

    As you wrote the duty cycle will be limited by the bandwidth of the
    MDC/MDIO register accesses.
    We are still evaluating whether this method increases the lifespan.

    Regards
    paddu

    I looked up the data sheet and found section 2.4 LED Interface and most likely you would want to select Mode 2 for the Table 3. LED Mode Select

    You may want to look at the resistors used with the LEDs as different values can lower the current/brightness and potentially extend the life of the LEDs since the diagram shows the LED and 110 ohm in parallel with 2.2k ohm resistor.  It also mentions the control register blinking the activity LED, but not in detail enough to tell if it would be an acceptable rate for your application.