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Chapter 5

Using the Client-side GMII Data Path

This chapter provides general guidelines for creating designs using client-side GMII of the Ethernet 1000BASE-X PCS/PMA or SGMII core.

Designing with the Client-side GMII for the 1000BASE-X Standard

It is not within the scope of this document to define the Gigabit Media Independent Interface (GMII)— see clause 35 of the IEEE 802.3 specification for information about the GMII. Timing diagrams and descriptions are provided only as an informational guide.

GMII Transmission

This section includes figures that illustrate GMII transmission. In these figures the clock is not labeled. The source of this clock signal varies, depending on the options selected when the core is generated. For more information on clocking, see Chapters 6, 7 and 8.

Normal Frame Transmission

Normal outbound frame transfer timing is illustrated in Figure 5-1. This figure shows that an Ethernet frame is proceeded by an 8-byte preamble field (inclusive of the Start of Frame Delimiter (SFD)), and completed with a 4-byte Frame Check Sequence (FCS) field. This frame is created by the MAC connected to the other end of the GMII. The PCS logic itself does not recognize the different fields within a frame and will treat any value placed on gmii_txd[7:0] within the gmii_tx_en assertion window as data.

gmii_txd[7:0]preamble

SFD

FCS

gmii_tx_en

gmii_tx_er

Figure 5-1:GMII Normal Frame Transmission

Ethernet 1000BASE-X PCS/PMA or SGMII v9.1

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UG155 March 24, 2008

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Xilinx 1000BASE-X manual Using the Client-side Gmii Data Path, Gmii Transmission, Normal Frame Transmission