L- and H-Tile Transceiver PHY User Guide

ID 683621
Date 1/30/2024
Document Table of Contents Byte Deserializer Deserialize x2 Mode

The deserialize x2 mode is used in high-speed applications such as the PCIe Gen1 or Gen2 protocol implementation, where the FPGA fabric cannot operate as fast as the RX PCS.

In deserialize x2 mode, the byte deserializer deserializes 8-bit, 10-bit (when the 8B/10B encoder is not enabled), 16-bit, and 20-bit (when the 8B/10B encoder is not enabled) input data into 16-bit, 20-bit, 32-bit, and 40-bit data, respectively. As the parallel data width from the word aligner is doubled, the clock rate is halved.

Note: Depending on when the receiver PCS logic comes out of reset, the byte ordering at the output of the byte deserializer may or may not match the original byte ordering of the transmitted data. The byte misalignment resulting from byte deserialization is unpredictable because it depends on which byte is being received by the byte deserializer when it comes out of reset. Implement byte ordering logic in the FPGA fabric to retain the order of transmitted data.