Altera Cyclone IV - Miscellaneous Transmitter PCS Features

1–8 Chapter 1: Cyclone IV Transceivers Architecture
Transmitter Channel Datapath
Cyclone IV Device Handbook, February 2015 Altera Corporation
Volume 2
at time n + 2 is encoded as a positive disparity code group. In the same example, the
current running disparity at time n + 5 indicates that the K28.5 in time n + 6 should be
encoded with a positive disparity. Because
tx_forcedisp is high at time n + 6, and
tx_dispval is high, the K28.5 at time n + 6 is encoded as a negative disparity code
group.
Miscellaneous Transmitter PCS Features
The transmitter PCS supports the following additional features:
■ Polarity inversion—corrects accidentally swapped positive and negative signals
from the serial differential link during board layout by inverting the polarity of
each bit. An optional
tx_invpolarity port is available to dynamically invert the
polarity of every bit of the 8-bit or 10-bit input data to the serializer in the
transmitter datapath. Figure 1–9 shows the transmitter polarity inversion feature.
1
tx_invpolarity is a dynamic signal and might cause initial disparity errors
at the receiver of an 8B/10B encoded link. The downstream system must be
able to tolerate these disparity errors.
Figure 1–9. Transmitter Polarity Inversion
Converted data output to the
transmitter serializer
Output from transmitter PCS
0
1
1
1
0
0
1
0
0
0
MSB
tx_invpolarity = HIGH
LSB
1
0
0
0
1
1
0
1
1
1
MSB
LSB