Altera Corporation
2–207
October 2007
Stratix II GX Device Handbook, Volume 2
Stratix II GX Transceiver Architecture Overview
Figure 2–153. Stratix II GX Block in PCI Express PIPE Reverse Parallel Loopback Mode
Reverse Serial Loopback
Reverse serial loopback is a subprotocol in Basic mode. It requires
8B/10B, and the word aligner pattern of K28.5. No dynamic pin control is
available to select or deselect reverse serial loopback. The active block of
the transmitter is only the buffer. The data sent to the receiver is retimed
with the recovered clock and sent out to the transmitter.
The data path for reverse serial loopback is shown in
Figure 2–154
. Data
comes in from the
rx_datain
ports in the receiver. The data is then fed
through the CDR block in serial form directly to the
tx_dataout
ports
in the transmitter block.
You can enable reverse serial loopback for all channels through the
MegaWizard. Any pre-emphasis setting on the transmitter buffer is
ignored in reverse serial loopback. The data flows through the active
blocks of the receiver and into the logic array.
Reverse serial loopback is often implemented when using a bit error rate
tester (BERT).
Transmitter Digital Logic
Receiver Digital Logic
Analog Receiver and
Transmitter Logic
FPGA
Logic
Array
BIST
Incremental
Generator
TX Phase
Compensation
FIFO
RX Phase
Compen-
sation
FIFO
Byte
Serializer
8B/10B
Encoder
Serializer
BIST
PRBS
Verify
Clock
Recovery
Unit
Word
Aligner
Deskew
FIFO
8B/10B
Decoder
Byte
De-
serializer
Byte
Ordering
BIST
Incremental
Verify
Rate
Match
FIFO
De-
serializer
BIST
PRBS
Generator
20
PCI Express PIPE
Reverse Parallel
Loopback