[En-Nut-Discussion] Problem with ETH PHY Lan8742

Ole Reinhardt ole.reinhardt at embedded-it.de
Wed Aug 31 12:12:51 CEST 2016

Hi Uwe,

Am 31.08.2016 um 11:38 schrieb Uwe Bonnes:
> while the Phy Lan8742A on the STM32 Discovery Boards works, on my 
> NUCLEO-F746ZG restarting often does not work and on NUCLEO-F767ZI
> boards even starting only works on rare occasions.

You mean that on the NUCLEO-F746ZG, the Phy works after power up, but
fails after a reset and on the other Nucleo Board it often fails?

I do not know these boards, nor their schematic. But pon the LPC boards,
that I designed, I connected the reset line of the PHY to a GPIO pin of
the CPU. This allowes me, to configure the MII lines as GPIO with
pullups set to the right strap values and the reset the phy manually.
This code is added to the board startup code, so that the MII interface
is later configured automatically correctly when the ethernet device is

> One problem I see is the content of the BMCR register after startup.
> Bits 13/12/8 should be set by the strap option, but often vary. The
> bits should be captured with reset deasserted, and a quick view with
> the scope does not show an obvious problem with the reset waveform.
> Has anybody seen problems with captured strap values on PHYS?

Not really. But I can imagine problems with the default configuration of
the MII pins of the CPU during CPU reset. That's the reason for the
above mentioned PHY reset code, that I added in my project.

Best regards,


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