Cyclone V Device Handbook: Volume 2: Transceivers

ID 683586
Date 10/24/2018
Document Table of Contents Receiver Byte Reversal

In double-width mode, two symbols of incoming data at the receiver may be accidentally swapped during transmission. For a 16-bit input data width at the word aligner, the two symbols are bits[15:8] and bits[7:0]. For a 20-bit input data width at the word aligner, the two symbols are bits[19:10] and bits[9:0]. The byte reversal feature at the word aligner output corrects the swapped signal error by swapping the two symbols in double-width mode at the word aligner output, as listed in Byte Reversal Feature.

Table 26.  Byte Reversal Feature
Byte Reversal Option Word Aligner Output
16-bit Data Width 20-bit Data Width
Disabled D[15:0] D[19:0]
Enabled D[7:0], D[15:8] D[9:0], D[19:10]

The reversal is controlled dynamically using the rx_bytereversal_enable register, and when you enable the receiver byte reversal option, this may cause initial disparity errors at the receiver with 8B/10B-coded data. The receiver must be able to tolerate these disparity errors.

Note: When receiving swapped symbols, the word alignment pattern must be byte-reversed accordingly to match the incoming byte-reversed data.