Xilinx Virtex-5 RocketIO GTP User Manual

Virtex-5 RocketIO GTP Transceiver User Guide www.xilinx.com 117
UG196 (v1.3) May 25, 2007
PCI Express Receive Detect Support
R
There are no attributes in this section.
Description
The PCI Express specification includes a feature that allows the transmitter on a given link
to detect if a receiver is present. The decision if a receiver is present is based on the rise time
of TXP/TXN. Figure 6-15 shows the circuit model used for receive detection. The GTP
transceiver must be in the P1 powerdown state to perform receiver detection. Also receiver
detection requires a 75 to 200 nF external coupling capacitor between the transmitter and
receiver, and the receiver must be terminated to GND.
The detection sequence starts with the assertion of TXDETECTRX. In response, the receive
detect logic drives TXN and TXP to V
DD
–V
SWING
/2 and then releases them. After a
programmable interval, the levels of TXN and TXP are compared with a threshold voltage.
At the end of the sequence, RXSTATUS and PHYSTATUS reflect the results of the receiver
detection.
TXDETECTRX0
TXDETECTRX1
In TXUSRCLK2
Activates the receive detection sequence. The sequence ends when
PHYSTATUS is asserted to indicate that the results of the test are
ready on RXSTATUS.
TXPOWERDOWN0[1:0]
TXPOWERDOWN1[1:0]
RXPOWERDOWN0[1:0]
RXPOWERDOWN1[1:0]
In Async
Controls the power state of the TX and RX links. The encoding
complies with the PCI Express encoding. TX and RX can be powered
down separately. However, for PCI Express compliance,
TXPOWERDOWN and RXPOWERDOWN must be used together.
00: P0 (normal operation)
01: P0s (low recovery time powerdown)
10: P1 (longer recovery time/RecDet still on)
11: P2 (lowest power state)
Table 6-19: PCI Express Receive Detect Support Ports (Continued)
Port Dir Domain Description
Figure 6-15: Receive Detection Circuit Model
C
CH
: < 3 nF
UG196_c6_15_080806
C
AC
: 75-200 nF
R
TERMR
: 40-60Ω
V
TERMR
R
TERMT
: 40-60Ω
V
DD
TXDETECTRX
GTP Transceiver
Components
Channel
Components
Far-End Receiver
Components
TXP

Xilinx Virtex-5 RocketIO GTP Specifications

General

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