The Odd Transmission Case - 16.2 English

1G/2.5G Ethernet PCS/PMA or SGMII LogiCORE IP Product Guide (PG047)

Document ID
Release Date
16.2 English

The following figure shows 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 device-specific 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. 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.

Note: The first Idle to follow the frame termination sequence will be a /I1/ if the frame ended with positive running disparity or a /I2/ if the frame ended with negative running disparity. This is shown as the shaded code group.
Figure 1. 1000BASE-X Transmit State Machine Operation (Even Case) gmii_txd[7:0] gmii_tx_en gmii_tx_er FCS FCS I2 I2 I2 T R I1/I2 R tx_code_group PCS Transmit Engine Encoding X12907