The GTM transmitter supports two types of binary encoding options, linear coding and Gray coding. By using gray coding, only one bit error per symbol is made for incorrect decisions, thus reducing the bit-error rate by more than 33%. The following figure illustrates the differences between linear coding and Gray coding.
Figure 1. Transmitted PAM4 Signal Bit Encoding
The TX gray encoder has independent endianness control blocks. The following figure shows the sequence in which bits are flipped.
Figure 2. TX Gray Encoder Bit Flip Sequence