RXUSRCLK2 is the main synchronization clock for all signals into the RX side of the GTM
transceiver. Most signals into the RX side of the GTM transceiver are sampled on the positive
edge of RXUSRCLK2. RXUSRCLK2 and RXUSRCLK have a fixed-rate relationship based on the
RX_DATA_WIDTH and RX_INT_DATA_WIDTH settings. The following table shows the
relationship between RXUSRCLK2 and RXUSRCLK per the RX_DATA_WIDTH and
RX_INT_DATA_WIDTH values.
Table 70: RXUSRCLK2 Frequency Relationship to RXUSRCLK
Encoding
RX Data Width
RX Internal
Datapath
RXUSRCLK2 Frequency
NRZ
64
64
F
RXUSRCLK2
= F
RXUSRCLK
128
64
F
RXUSRCLK2
= F
RXUSRCLK
/2
PAM4
80
80
F
RXUSRCLK2
= F
RXUSRCLK
160
80
F
RXUSRCLK2
= F
RXUSRCLK
/2
128
128
F
RXUSRCLK2
= F
RXUSRCLK
256
128
F
RXUSRCLK2
= F
RXUSRCLK
/2
These rules about the relationships between clocks must be observed for RXUSRCLK and
RXUSRCLK2:
• RXUSRCLK and RXUSRCLK2 must be positive-edge aligned, with as little skew as possible
between them. As a result, low-skew clock resources (BUFG_GTs) must be used to drive
RXUSRCLK and RXUSRCLK2.
• If the channel is configured so that the same oscillator drives the reference clock for the
transmitter and the receiver, TXPROGDIVCLK can be used to drive RXUSRCLK and
RXUSRCLK2 in the same way that they are used to drive TXUSRCLK and TXUSRCLK2.
• If separate oscillators are driving the reference clocks for the transmitter and receiver on the
channel, RXUSRCLK and RXUSRCLK2 must be driven by RXPROGDIVCLK.
Ports and Attributes
The following table defines the TX interface ports.
Table 71: RX Interface Ports
Port
Dir
Clock Domain
Description
RXDATA[255:0]
Out
RXUSRCLK2
The bus for receiving data. The width of this port is
equal to RX data width selection. RX data width
selection:
64: RXDATA[63:0]
80: RXDATA[79:0]
128: RXDATA[127:0]
160: RXDATA[159:0]
256: RXDATA[255:0]
Chapter 4: Receiver
UG581 (v1.0) January 4, 2019
Virtex Ult GTM Transceivers
115