MDIO Functions

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MDIO is a Management Data Input/Output Interface defined in IEEE 802.3 Clause 22 and extended in Clause 45. It is two signal based interface between Station Management (SUB-20 in our case) and a Physical Layer device (PHY). Where a PHY, or grouping of PHY's, is an individually manageable entity, known as an MDIO Manageable Device (MMD).


MDC - management data clock. MDC is sourced by SUB-20 to the PHY as the timing reference for transfer of information on the MDIO signal.

MDIO - management data input/output. MDIO is a bidirectional signal between PHY and the SUB-20 It is used to transfer control information and status between the PHY and the SUB-20. Control information is driven by the SUB-20 synchronously with respect to MDC and is sampled synchronously by the PHY. Status information is driven by the PHY synchronously with respect to MDC and is sampled synchronously by the SUB-20.

Frame Format

SUB-20 supports both MDIO frame formats defined in  IEEE 802.3 Clause 22 and Clause 45.



Clause 22 MDIO frame format




Clause 45 MDIO frame format




Beginning from FW version 0.2.8 and library version, additional MDIO1 channel is available on SPI header ( see SPI Header ). To access MDIO1 channel use sub_mdio_xfer_ex function with channel=1.

CFP MSA Support

Beginnig from FW version 0.3.2 and library version, SUB-20 supports CFP MSA compatible transactions at 4MHz MDC frequency. See sub_mdio_xfer_ex.




sub_mdio_xfer, sub_mdio_xfer_ex