Parallel Loopback; Post/Pre-Driver Serial Loopback; Table 5-4: Recommended Settings For Serial Loopback - Xilinx RocketIO X User Manual

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Parallel Loopback

In parallel loopback mode, data is looped at the PCS/PMA interface and clocked via the
synthesized clock from the RocketIO X transmitter. A stable REFCLK and valid PMA
initialization are required.
In parallel loopback mode, TXINHIBIT can not be used to suppress the transmit data from
being sent onto the TXN/TXP pins, because TXINHIBIT also inhibits the data being
looped back to the receiver. The pre-driver serial loopback mode should be used for
applications that do not require any data to be driven onto the transmit pins.
Note:

Post/Pre-Driver Serial Loopback

Since the serial-loopback mode test-data paths are internal to the silicon, certain
equalization default settings optimized for a complete system can cause improper
operation when using serial loopback. The modes that need different settings for serial
loopback are shown in
addresses of the PMA Attribute Bus (see
Bus").
Pre-driver serial loopback does not switch the TXN and TXP. It also does not require TXN
and TXP to be terminated. However, post-driver serial loopback does require proper
termination of TXN/TXP for proper operation

Table 5-4: Recommended Settings for Serial Loopback

128
TXPOLARITY/RXPOLARITY have no effect on the parallel loopback operation.
Table 5-4, along with the recommended settings for specific
Mode
20_XX (6.25G)
30_XX (2/48G)
28_XX (2.56G)
25_XX (3.125G)
13_XX (10G)
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Chapter 5: Simulation and Implementation
Appendix C, "PMA Attribute Programming
PMA Address
0 x OC
0 x OD
RocketIO™ X Transceiver User Guide
UG035 (v1.5) November 22, 2004
Recommended Value
OD
FC