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Chapter 7: GTP Receiver (RX)
Configurable Termination Impedance
To minimize distortion due to reflections, the termination impedance of each receiver must
be matched as closely as possible to the impedance of the serial trace to which it is
connected. See
termination impedance is calibrated.
Configurable Termination Voltage
As shown in
through the calibrated line termination impedances to one of three termination voltages:
GND, MGTAVTTRX, or 2/3 MGTAVTTRX (from the GTP receiver). At any given time,
only one of these connections is active.
The appropriate RX termination voltage is selected based on the type of coupling used, the
TX termination voltage, and the requirements of the protocol being used.
summarizes the termination options available in the GTP receiver.
activate the different RX termination options.
Table 7-3: Recommended RX Termination Settings
Table 7-4: RX Termination Attribute Settings
128
Chapter 10, "GTP-to-Board Interface,"
Figure
7-2, the line termination circuit connects the RXP and RXN pads
Valid RX
Coupling Type
Termination
Settings
2/3 MGTAVTTRX,
DC coupled
MGTAVTTRX
External AC
2/3 MGTAVTTRX
coupling only
MGTAVTTRX,
Built-in AC
2/3 MGTAVTTRX,
coupling only
GND
Built-in AC
MGTAVTTRX,
and external
2/3 MGTAVTTRX,
AC coupling
GND
RX Termination Voltage
MGTAVTTRX
2/3 MGTAVTTRX
GND
www.xilinx.com
for more information about how the
Notes
The TX termination (and TX termination voltage)
must match the selected RX termination (and RX
termination voltage) to prevent DC currents.
2/3 MGTAVTTRX is optimal for the receiver.
Recommended configuration because it permits
connections to the widest variety of transceivers
including hotswap applications.
The RX termination (and RX termination voltage)
must match the TX termination (and TX termination
voltage) to prevent DC currents.
The built-in AC-coupling capacitors do not block a DC
current path between the RX termination of the
receiver and the TX termination of the transmitter.
Only an external AC-coupling capacitor will prevent a
DC current path between the transmitter's TX
termination and the receiver's RX termination.
Use GND to support the PCI Express TXDETECTRX
feature. See
"PCI Express Receive Detect Support,"
page
108.
RCV_TERM_GND
FALSE
FALSE
TRUE
Virtex-5 RocketIO GTP Transceiver User Guide
R
Table 7-3
Table 7-4
shows how to
RCV_TERM_VTTRX
TRUE
FALSE
FALSE
UG196 (v1.3) May 25, 2007
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