The sampled eye diagram is constructed by plotting one sample per symbol located at the CDR
sampling point (after the equalizer). By plotting multiple samples, the image looks like the figure
above. Sampled eye supports both NRZ and PAM4 modulation, with the only difference being
that the NRZ eye consists of two amplitude margin levels, and PAM4 with four distinct amplitude
margin levels.
RX Pre-Coder
Ult GTM receiver supports pre-coding. Pre-coding can be used to reduce receiver DFE
error propagation by reducing 1-tap burst error runs into two errors for every error event.
Ports and Attributes
The following table defines the attributes required for RX pre-coder control.
Table 57: Pre-Coder Attributes
Attribute
Type
Description
CH[0/1]_RX_PCS_CFG0
16-bit
Reserved.
Bit Name
Address
Description
RX_PRECODE_ENDIAN
[11]
In PAM4 mode, this attribute controls pre-coder
received endianness. In NRZ mode, the default
Wizard value must be used.
1’b0
: Non-inverting.
1’b1
: Inverting.
RX_PRECODE_BYP_EN
[10]
In PAM4 mode, this attribute enables pre-coding. In
NRZ mode, the default Wizard value must be used.
1’b0
: Enables pre-code.
1’b1
: Disables pre-code.
IMPORTANT! In PAM4 mode, if the pre-coder is enabled for the receiver, the transmitter pre-coder
should also be enabled for proper data recovery.
RX Gray Encoder
The Ult FPGA GTM receiver supports two types of binary enconding options: linear 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%.
illustrates the differences between
linear and Gray Coding.
Chapter 4: Receiver
UG581 (v1.0) January 4, 2019
Virtex Ult GTM Transceivers
99