Regarding MII spec, I have a question about the RX_DV signal that I'm not able to find elsewhere: From the perspective of the Ethernet MAC, when sending a frame to a PHY over MII, does the RX_DV (Data Valid) signal have to stay HIGH/asserted for the entire frame, or can it go LOW and back HIGH again on the same frame (and still be interpreted as 1 frame by the PHY)?

I guess another way of asking is: does an MII PHY use the RX_DV as a delimiter for individual frames, or does it check the SOF byte of something else to distinguish frames?

Any help is appreciated


The MII is specified in IEEE 802.3 Clause 22. You can get it for free after registration on IEEE GET.

RX_DV is asserted when the preamble is detected, and it is deasserted at the end of the frame, see Clause for details:

RX_DV (Receive Data Valid) is driven by the PHY to indicate that the PHY is presenting recovered and decoded nibbles on the RXD<3:0> bundle and that the data on RXD<3:0> is synchronous to RX_CLK. RX_DV shall transition synchronously with respect to the RX_CLK. RX_DV shall remain asserted continuously from the first recovered nibble of the frame through the final recovered nibble and shall be negated prior to the first RX_CLK that follows the final nibble. In order for a received frame to be correctly interpreted by the Reconciliation sublayer and the MAC sublayer, RX_DV must encompass the frame, starting no later than the Start Frame Delimiter (SFD) and excluding any End-of-Frame delimiter.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.