I have a custom board(designed by us) based on IMX6 SoloX. This board has (among other) two optical ports 100-FX, realized connecting a micrel KSZ8873FLLI via MII to the SoloX.
The problem is that I found an unexpected electrical level on the MII interface in TX direction. I would like the high level to be 3.3V, but on the oscilloscope I quite often can see a stable level around 2 volts.
So on the TX line I can see 3 different voltage level: 3.3V (expected igh level), 2V (unexpected and unwanted high level), and 0V (low level).
Of course with this condition the port is not working.
My question are:
1) Is it possibile for the SoloX to work with an MII interface with 3.3V as high level ? The reference manual is not very clear on this topic.
2) If yes, how the NVCC_SGMII should be connected ?
3) What can cause this strange 3 level signal ?