Preamble Shrinkage - 16.2 English

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

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16.2 English
As previously described, a single byte of preamble can be lost across the 1000BASE-X system (the actual loss occurs in the 1000BASE-X PCS transmitter state machine).
  • There is no specific statement for this preamble loss in the IEEE 802.3-2008 specification; the preamble loss falls out as a consequence of the state machines (see figures 36-5 and 36-6 in the IEEE 802.3-2008 specification).
  • IEEE 802.3ah-2004 does, however, specifically state in clause
Note: The 1000BASE-X PCS transmit function replaces the first octet of preamble with the /S/ code-group or it discards the first octet and replaces the second octet of preamble with the /S/ code-group. This decision is based upon the even or odd alignment of the PCS transmit state diagram (see Figure 36-5)."