The Intel® Management Data Input/Output (MDIO) PHY management bus has two signals per MAC: MDC and MDIO. MDC is the clock output, which is not free running. At 2.5 MHz, it has a 400 ns minimum period. MDIO is a bidirectional data signal with a High-Z bus turnaround period.
When the MAC writes to the PHY, the data is launched on the falling edge, meaning there is 200 ns -10 ns = 190 ns for flight time, signal settling, and setup at the receiver. Because data is not switched until the following negative edge, there is also 200 ns of hold time. These requirements are very easy to meet with almost any board topology. When the MAC reads from the PHY, the PHY is responsible to output the read data from 0 to 300 ns back to the MAC, leaving 100 ns less 10 ns setup time, or 90 ns for flight time, signal settling, and setup at the receiver. This requirement is also very easy to meet.
GUIDELINE: Board pull-ups on MDC/MDIO.
Both signals require an external pull-up resistor. Consult your PHY's datasheet for the correct pull-up resistor value. 1K Ohm is a typical resistor value.
GUIDELINE: Ensure interface timing that MDIO requires.
MDIO requires a 10 ns setup and hold time for data with respect to MDC. For specific values, refer to the Intel Agilex® 7 FPGA Data Sheet.
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