imx8mm pin AB23 (used as MX8MM_IOMUXC_SD2_DATA0_GPIO2_IO15) doesn't work in push pull config

[jochen_albert]

Hello,

we have a Microchip LAN9253 attached to some inputs of the imx8mm. 2 other signals from the chip were already attached in the past and worked fine when set to push pull.

All Input pads on the imx8mm side are set to 0x16. So no pull up or pull own enabled.

On the newly added signal to pin AB23 (set to MX8MM_IOMUXC_SD2_DATA0_GPIO2_IO15) we see in that configuration only a very weak signal with a few milliVolt:

see

thumbnail_image001.png

When we switch the output of the LAN9253 to open drain, please note that no pull up or down is selected on the imx8mm nor is there any external pull up or pull down, we see some kind of 3,3V volt signal. Not the best signal, degrading a bit over time:

see thumbnail_image002.png

So where do here the 3.3V come from? Is there anything on imx8mm side that would explain how that config can be working. And why the Push Pull config isn't working?

If we additionally enable a pull up on the imx8mm side, we get a good looking signal. But we would like to understand what is happening here.

Thanks,

Jochen Albert

[JorgeCas]

Hello, I hope you are doing well.

I do not see something wrong on you IOMUX and Pad Control registers, it should be configured as GPIO and Pull-up/No Pull-up.

Since is an output from the LAN9253 I suggest you check with other PHYs .

Are you still having 3.3v noisy signal when is not connected to the PHY and configured with Pull-up.

Best regards.