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Ethernet 1000BASE-X PCS/PMA or SGMII v9.1
UG155 March 24, 2008
Chapter 5:
Using the Client-side GMII Data Path
R
10 Megabit per Second Frame Transmission
The operation of the core remains unchanged. It is the responsibility of the client logic (for
example, an Ethernet MAC), to enter data at the correct rate. When operating at a speed of
10 Mbps, every byte of the MAC frame (from destination address to the frame check
sequence field, inclusive) should each be repeated for 100 clock periods to achieve the
desired bit rate. It is also the responsibility of the client logic to ensure that the interframe
gap period is legal for the current speed of operation.
GMII Reception
1 Gigabit per Second Frame Reception
The timing of normal inbound frame transfer is illustrated in
Figure 5-12
. At 1 Gbps speed,
the operation of the receiver GMII signals remains identical to that described in
“Designing with the Client-side GMII for the 1000BASE-X Standard” in Chapter 5
.
100 Megabit per Second Frame Reception
The operation of the core remains unchanged. When operating at a speed of 100 Mbps,
every byte of the MAC frame (from destination address to the frame check sequence field,
inclusive) is repeated for 10 clock periods to achieve the desired bit rate. See
Figure 5-13
. It
is the responsibility of the client logic, for example an Ethernet MAC, to sample this data
correctly.
Figure 5-12:
GMII Frame Reception at 1 Gbps
gmii_rxd[7:0]
gmii_rx_dv
gmii_rx_er
preamble
FCS
SFD
D0
D1
userclk2
Figure 5-13:
GMII Data Reception at 100 Mbps
gmii_rxd[7:0]
gmii_rx_dv
gmii_rx_er
preamble
SFD
D0
D1
10 clock periods
userclk2
