Configurable Termination Impedance; Txinhibit - Xilinx Virtex-5 RocketIO GTP User Manual

R
The pre-emphasis technique used by the GTP transceiver is de-emphasis. When a serial bit
is repeated, the power of the repeated bit is reduced. For example, if two ones are sent in a
row, the power of the second one is reduced compared to the first. The power of slowly
changing signals (the low-frequency components) is reduced relative to quickly changing
signals (the high-frequency components). Refer to
pages 211-215, for more detailed explanations of pre-emphasis and de-emphasis.
Each GTP transceiver has a TXPREEMPHASIS port for controlling pre-emphasis.
Table 6-18
each TXPREEMPHASIS level. The higher the percentage, the more de-emphasis is applied.
Be careful not to overcompensate for high-frequency losses. Using too much pre-emphasis
can cause signal distortion, and combining pre-emphasis with RX equalization (see
Termination and Equalization," page
in the channel.

Configurable Termination Impedance

The termination impedance of each transmitter must be matched as closely as possible to
the impedance of the serial trace it is driving to minimize distortion due to reflections. See
Chapter 10, "GTP-to-Board Interface,"
impedance is calibrated.

TXINHIBIT

The TX driver includes the TXINHIBIT port. When TXINHIBIT is driven High, the TX
driver stops sending data and transmits only a differential 0 value (TXP High, TXN Low).
Virtex-5 RocketIO GTP Transceiver User Guide
UG196 (v1.3) May 25, 2007
shows the percentage decrease of signal amplitude for de-emphasized bits at
www.xilinx.com
[Ref 4], pages 465-471, and
125) can over-emphasize the high-frequency signal
for more information about how the termination
Configurable TX Driver
[Ref 5],
"RX
115