DP83848K: DP83848K Speed LED ON all the time

Gump

Part Number: DP83848K

When use DP83848K, i found the LED in "LED_SPEED" pin is on all the time, regardless of "LED_SPEED" and "LED_LINK" pullup/pulldown, even if unplug the network cable.

Does it possible caused by LEDCR? What does the sentence "The register(LEDCR) does not provide read access to the LED" mean?

over 8 years ago

0 Gump over 8 years ago

Intellectual 490 points

Hi, could anybody tell me if SPEED LED always on is a normal state?

0 Ross Pimentel over 8 years ago in reply to Gump

TI__Mastermind 23675 points

Hi,

Are you forcing the PHY to 100Mbps operation?
If you are then SPEED_LED will be ON.

Kind regards,
Ross

0 Gump over 8 years ago in reply to Ross Pimentel

Intellectual 490 points

Dear Ross,
Thanks for your response!
Moreover, SPEED LED will be ON as soon as DP83848 is powered?

0 Ross Pimentel over 8 years ago in reply to Gump

TI__Mastermind 23675 points

Hi Gump,

Yes, if the device is configured for 100Mbps. The SPEED LED will be ON for 100Mbps operation and OFF for 10Mbps operation.
This is regardless of link.

Kind regards,
Ross

0 Bal Soora over 8 years ago in reply to Ross Pimentel

Prodigy 10 points

Hi,

We are having the same issue - the speed LED is on all the time. The circuit we used is the one in the datasheet dp83848K page 30. This is the one with no strap on LED_SPEED and a 2.2K strap to ground on the LED_LINK. We have a third party driver and am not sure if any config bits (such as AN0 and AN1) are set by the driver. Assuming only the straps are used to set config, what is the expected behaviour of the LEDs? Since LED_SPEED is on all the time does that mean it is configured for 100 mbits all the time?

0 Rob Rodrigues over 8 years ago in reply to Bal Soora

TI__Mastermind 19780 points

Hi Bal,

When we have auto-negotiation enabled, the PHY uses the 100M receiver which causes LED_SPEED to be illuminated, even when no link is present.

The LED will be extinguished only when the PHY is in 10M mode. This has to be done by a 10M link OR disabling auto-negotiation and setting the speed to 10M.

Best Regards,

Interface

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DP83848K: DP83848K Speed LED ON all the time