188.8.131.52. 64B/66B Encoder and Transmitter State Machine (TX SM)
The 64B/66B encoder is used to achieve DC-balance and sufficient data transitions for clock recovery. It encodes 64-bit XGMII data and 8-bit XGMII control into 10GBASE-R 66-bit control or data blocks in accordance with Clause 49 of the IEEE802.3-2008 specification.
The 66-bit encoded data contains two overhead sync header bits that the receiver PCS uses for block synchronization and bit-error rate (BER) monitoring. The sync header is 01 for data blocks and 10 for control blocks. Sync headers are not scrambled and are used for block synchronization. (The sync headers 00 and 11 are not used, and generate an error if seen.) The remainder of the block contains the payload. The payload is scrambled and the sync header bypasses the scrambler.
The encoder block also has a state machine (TX SM) designed in accordance with the IEEE802.3-2008 specification. The TX SM ensures valid packet construction on data sent from the MAC layer. It also performs functions such as transmitting local faults under reset, as well as transmitting error codes when the 10GBASE-R PCS rules are violated.