Xilinx 1000BASE-X - Manual (Page 214)

214 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 Odd Case
Figure D-4 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.
Note that the Start of Packet code group /S/ is again replaced with a preamble byte.
However, the first preamble byte of the original transmit GMII (see
Figure D-3 ) frame
(which was replaced with the /D16.2/ character to complete the Idle sequence), has not
been replaced. This has resulted in a single byte of preamble loss across the system.
Figure D-3: 1000BASE-X Transmit State Machine Operation (Odd Case)
gmii_txd[7:0]
gmii_tx_en
gmii_tx_er
preamble
SFD
preamble
SFD
tx_code_group I2 I2 I2 S
PCS Transmit Engine Encoding
Figure D-4: 1000BASE-X Reception State Machine Operation (Odd Case)
gmii_rxd[7:0]
gmii_rx_dv
gmii_rx_er
preamble
SFD
preamble
SFD
rx_code_group I2 I2 I2 S
PCS Receive Engine Decoding