2–42
Altera Corporation
Stratix II GX Device Handbook, Volume 2
October 2007
Transmitter Modules
Figure 2–35. Transmitter Force Disparity Feature in Double-Width Mode
Transmitter Polarity Inversion
The positive and negative signals of a serial differential link might
accidentally be swapped during board layout. Solutions like a board
re-spin or major updates to the PLD logic can prove expensive. The
transmitter polarity inversion feature is provided to correct this situation.
An optional
tx_invpolarity
port is available in all single-width and
double-width modes except (OIF) CEI PHY to dynamically enable the
transmitter polarity inversion feature. In single-width modes, a high
value on the
tx_invpolarity
port inverts the polarity of every bit of
the 8-bit or 10-bit input data word to the serializer in the transmitter data
path. In double-width modes, a high value on the
tx_invpolarity
port
inverts the polarity of every bit of the 16-bit or 20-bit input data word to
the serializer in the transmitter data path. Since inverting the polarity of
each bit has the same effect as swapping the positive and negative signals
of the differential link, correct data is seen by the receiver. The
tx_invpolarity
is a dynamic signal and may cause initial disparity
errors at the receiver of an 8B/10B encoded link. The downstream system
must be able to tolerate these disparity errors.
Current Disparity
clock
tx _ in [ 15 : 0 ]
tx _ forcedisp [1 : 0 ]
BC BC
BC BC
BC
BC BC
tx _ ctrlenable [1 :0 ]
BC
Encoded Value
17C
283
17C
283
283
283
17C
17C
RD-
RD +
RD+
RD-
RD+
RD-
RD+
RD-
n
n+ 2
n + 4
n + 6
tx _ dispval [ 1 :0 ]
01
00
00
00