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I know that the maximum number of devices that can be connected via MDIO bus is 32. But how to determine the real maximum fanout of MDIO bus. I mean I have a PCB (6U size) that has AM335x SoC driving 7 ICs via MDIO. I'm concerned if AM335x SoC's MDIO module is able to deal with such a load (considering also that PCB traces are quite long, I think it's about 150-200 mm, which introduces (I think) additional load capacitance). How can I check that AM335x SoC device is able to deal with the load I've described? Which parameter from the datasheet should I point attention to? Or how can I check that on the PCB with the oscilloscope?

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The datasheets usually provide electrical characteristics what voltages to expect at given load current and what kind of rise/fall times to expect at given load capacitance.

You should sum up how much each chip will add load to the bus, and how much the bus length itself adds load.

If it sounds too theoretical, you can simply see what kind of bus waveforms there are when communicating with each of the devices. Then it's only a matter of checking if those voltages are within high and low thresholds of all the chips on the bus.

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  • \$\begingroup\$ Got it! Thank you! \$\endgroup\$ – Andy Nov 21 '20 at 15:58

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