Xilinx Virtex-5 RocketIO GTP User Manual

114 www.xilinx.com Virtex-5 RocketIO GTP Transceiver User Guide
UG196 (v1.3) May 25, 2007
Chapter 6: GTP Transmitter (TX)
R
Each of the pad drivers is driven by a pre-driver whose output amplitude is controlled by
TXBUFDIFCTRL. Although the pre-driver output swing does not change the output swing
at the TX pad, the inputs of TXBUFDIFCTRL and TXDIFFCTRL must always be tied
together.
Each GTP transceiver includes an additional attribute, TX_DIFF_BOOST, which can be
used to increase the maximum possible output swing. TX_DIFF_BOOST is set to FALSE
when additional output swing is required. TX_DIFF_BOOST is set to TRUE when the
output swing is acceptable and lower power consumption is desired.
Pre-Emphasis
Serial traces tend to attenuate high frequencies more than low frequencies. Pre-emphasis is
a technique used to equalize transmitted data. It compensates for the excess high-
frequency loss by transmitting high-frequency signals with more power than low-
frequency signals.
Table 6-17: Transmitter Output Swing
Port Value Transmitter Differential Swing (mV)
TXDIFFCTRL0[2:0] = TXBUFDIFFCTRL0[2:0]
TXDIFFCTRL1[2:0] = TXBUFDIFFCTRL1[2:0]
000 1100
001 1050
010 1000
011 900
100 800
101 600
110 400
111 0
Table 6-18: Transmitter Pre-Emphasis Settings
Port Value Transmitter Pre-Emphasis (%)
(1,2)
TXPREEMPHASIS0[2:0]
TXPREEMPHASIS1[2:0]
Pre-Emphasis Boost On
TX_DIFF_BOOST = FALSE
Pre-Emphasis Boost Off
TX_DIFF_BOOST = TRUE (Default Setting)
000 23
001 23
010 2.5 4
011 4.5 10.5
100 9.5 18.5
101 16 28
110 23 39
111 31 52
Notes:
1. Nominal values. Refer to the Virtex-5 Data Sheet for the exact values.
2. Refer to [Ref 5], pages 211-215 and [Ref 9], pages 465-471 for detailed explanations of pre-emphasis.

Xilinx Virtex-5 RocketIO GTP Specifications

General

Brand	Xilinx
Model	Virtex-5 RocketIO GTP
Category	Transceiver
Language	English