Hi Sid,
The issue here is that the DP83848TSQ is a current mode PHY. It’s designed to sink and source current through a transformer to generate the correct voltages for the ethernet signals.
This is in contrast to a voltage mode PHY, which directly generates the voltage levels for ethernet.
GigaBlox Nano is a voltage mode PHY, and can generally be interfaced with other voltage mode PHYs without needing transformers (transformerless ethernet).
But a current mode PHY will always need a transformer to work, which you don’t have in your design. So I wouldn’t expect this to work. There’s actually a related forum post on this which I’ve linked below.
To solve this, either add transformers to your design or switch to a voltage mode PHY (There are many options).
Side note - How do I know this is a current mode PHY? Looking at the example schematic in the datasheet for the DP83848TSQ, we can see that the center taps of the transformers are connected to 3.3V. That’s a key giveaway.
