Xilinx 1000BASE-X - Manual (Page 53)

Ethernet 1000BASE-X PCS/PMA or SGMII v9.1 www.xilinx.com 53
UG155 March 24, 2008
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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.
Figure 5-1: GMII Normal Frame Transmission
gmii_txd[7:0]
gmii_tx_en
gmii_tx_er
preamble FCS
SFD