DP83849I: How does LED_ACT pin behave?

user5286503

Part Number: DP83849I

Dear Support Team,

Regarding the LED_ACT pin, which one of the following [A], [B] and [C] is correct?

[A] LED_ACT pin (21-pin, 41-pin) blinks at a frequency of the B;O;ML_FREQ bit (LEDCR, bit[7:6]) when activity is on MII.

(According to Datasheet, we understood that LED_LINK pin blinks at the frequency of the B;O;ML_FREQ bit.

But we are not sure whether LED_ACT blinks at the frequency or not.)

[B] LED_ACT pin is asserted during the TX_EN_A/B or RX_DV_A/B is asserted.

[C] Other. Could you give us the condition at which LED_ACT pin is asserted?

Thank you.

over 4 years ago

0 Lucas Wolter over 4 years ago

TI__Mastermind 27950 points

Hi Takashi-san,

Please refer to section 5.3.3 in the datasheet for more information about how to configure LED_ACT. By default (mode 1), LED_ACT will act as an activity LED, meaning it will constantly stay ON if there is any RX or TX activity. This LED cannot be configured to blink, it will always either be high or low.

Please let me know if you have any other questions, otherwise I will close this thread.

Thanks,

Lucas

All information in this correspondence and in any related correspondence is provided “as is” and “with all faults”, and it is subject to TI’s Important Notice (http://www.ti.com/corp/docs/legal/important-notice.shtml).

0 user5286503 over 4 years ago in reply to Lucas Wolter

Prodigy 210 points

Dear Lucas-san,

Thank you for your quick response.

We understood that the LED_ACT does not blink and it will stay ON if activity is on TX or RX.

Could you give us the minimum ON width for the LED_ACT?

Is it about 40nsec which is a cycle of 25MHz clock used at MII interface?

Thank you.

Best regards,

Takashi

0 Lucas Wolter over 4 years ago in reply to user5286503

TI__Mastermind 27950 points

Hi Takashi-san,

We're looking into your question and will get back to you by Wednesday.

Thanks,

Lucas

0 Lucas Wolter over 4 years ago in reply to Lucas Wolter

TI__Mastermind 27950 points

Hi Takashi-san,

The minimum ON width of LED_ACT is not something we characterize. How will this information be useful?

Thanks,

Lucas

0 user5286503 over 4 years ago in reply to Lucas Wolter

Prodigy 210 points

Dear Lucas-san,

Thank you for your confirmation.

We will connect the LED_ACT signal to a CPLD which operates at 50MHz (cycle time=20ns) .

So we would like to confirm that the CPLD is able to sample all the assertion of the LED_ATC signal correctly.

*If the minimum assertion width of the LED_ACT is less than 20ns, the CPLD could miss sampling the assertion.

Thank you.

Best regards,

Takashi

0 Lucas Wolter over 4 years ago in reply to user5286503

TI__Mastermind 27950 points

Hi Takashi-san,

We're looking into this and will get back to you by Friday.

Thanks,

Lucas

0 Lucas Wolter over 4 years ago in reply to Lucas Wolter

TI__Mastermind 27950 points

Hi Takashi-san,

Although we don't characterize the minimum ON width of LED_ACT, this is something you can test by sending a quick burst to the PHY and measuring the ON pulse width of the LED.

Thanks,

Lucas

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DP83849I: How does LED_ACT pin behave?