CX11656 HomePlug 1.0 PHY Data Sheet
3.1.1.3
MII Frame Structure
The frame structure transmitted on the MII or GPSI interface is the following sequence of
fields:
Interframe Gap
Preamble
Start Frame
Delimiter Data
Interframe Gap
A period on the MII interface during which no data activity occurs on the MII.
Preamble
Begins a frame transmission that consists of 7 octets with the following bit values:
10101010 10101010 10101010 10101010 10101010 10101010 10101010
The preamble is stripped by the CX11656 when transmitting (the preamble is not
transmitted on the PLC medium) and pre-pended by the CX11656 when receiving.
Start Frame Delimiter
Indicates the start of a frame and follows the preamble. The SFD bit sequence is
10101011.
The start frame delimiter is stripped by the CX11656 when transmitting (the SFD is not
transmitted on the PLC medium) and pre-pended by the CX11656 when receiving
Data
Data sent over the MII interface consists of N bytes of data transmitted as 2N nibbles.
The de-assertion of the MII_TXEN signals the End Of Frame (EOF) for data transmitted
on the MII_TX[3:0] pins. Likewise, the de-assertion of the MII_RXDV signals the EOF
for data transmitted on MII_RX[3:0].
Figure 3-10. Partition of Serial Bit Stream to Nibble Stream
MACs Serial Bit Stream
LSb D0 D1 D2 D3 D4 D5 D6 D7 MSb
First nibble Second nibble
LSb D0
D1
MII
Nibble
Stream
D2
MSb D3
101409_014
3-8
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