Xilinx 1000BASE-X - Manual (Page 216)

216 www.xilinx.com Ethernet 1000BASE-X PCS/PMA or SGMII v9.1
UG155 March 24, 2008
Appendix D: 1000BASE-X State Machines R
Reception of the Even Case
Figure D-6 illustrates the reception of the in-bound code-group stream, received either
serially using the RocketIO transceiver, or in parallel across the TBI, and translation of this
code-group stream into the receiver GMII. This is performed by the PCS Receive Engine.
The Odd Transmission Case
Figure D-7 illustrates the translation of GMII encoding into the code-group stream
performed by the PCS Transmit Engine; this stream is transmitted out of the core, either
serially using the RocketIO transceiver, or in parallel across the TBI.
In response to the deassertion of gmii_tx_en, an End of Packet code group /T/ is
immediately inserted. Note that the even and odd alignment described in
“Start of Frame
Encoding” persists throughout the Ethernet frame. If the /T/ character occurs in the odd
position (the frame contained an odd number of bytes starting from the /S/ character),
then this is followed with two Carrier Extend code groups /R/. This allows the /K28.5/
character of the following Idle code group to be aligned to the even position.
Figure D-6: 1000BASE-X Reception State Machine Operation (Even Case)
gmii_rxd[7:0]
gmii_rx_dv
gmii_rx_er
FCS
FCS I2 I2 I2 T R I1/I2 rx_code_group
PCS Receive Engine Decoding