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Chapter 16: Transceiver Reconfiguration Controller IP Core 16–49
Loopback Modes
November 2012 Altera Corporation Altera Transceiver PHY IP Core
User Guide
Loopback Modes
You can enable the pre- and post-CDR reverse serial loopback modes by writing the
appropriate bits of the Transceiver Reconfiguration Controller
pma_offset
register
described in PMA Analog Registers. In pre-CDR mode, data received through the RX
input buffer is looped back to the TX output buffer. In post-CDR mode, received data
passes through the RX CDR and then loops back to the TX output buffer. The RX data
is also available to the FPGA fabric. In the TX channel, only the TX buffer is active.
Figure 16–14 illustrates these modes.
In addition to the pre-CDR and post-CDR loopback modes available in the
Transceiver Reconfiguration Controller register map, all the of PHYs, with the
exception of PCI Express, support serial loopback mode. You enable this mode by
writing the
phy
_
serial
_
loopback
register (0x061) using the Avalon-MM PHY
management interface. PCI Express supports reverse parallel loopback mode as
required by the PCI Express Base Specification.
Figure 16–14. Pre- and Post-CDR Reverse Serial Loopback Paths
(1)
Notes to Figure 16–14:
(1) Grayed-out blocks are not active in these modes.
(2) Post-CDR reverse serial loopback path.
(3) Pre-CDR reverse serial loopback path.
Tx PCS
Rx PCS
Tx PMA
Serializer
Rx PMA
Deserializer
To FPGA fabric
for verication
Transceiver
CDR
(2) (3)
FPGA
Fabric
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