EP4SE360F35I4 Datasheet, PDF (295/432 Pages) Altera Corporation – This section provides a complete overview of all features relating to the Stratix IV device family, which is the most architecturlly advanced

Chapter 8: High-Speed Differential I/O Interfaces and DPA in Stratix IV Devices
Differential Transmitter
8–15
Pre-emphasis is an important feature for high-speed transmission. Without
pre-emphasis, the output current is limited by the V_OD setting and the output
impedance of the driver. At high frequency, the slew rate may not be fast enough to
reach full V_OD before the next edge, producing pattern-dependent jitter.
With pre-emphasis, the output current is boosted momentarily during switching to
increase the output slew rate. The overshoot introduced by the extra current happens
only during switching and does not ring, unlike the overshoot caused by signal
reflection. The amount of pre-emphasis needed depends on the attenuation of the
high-frequency component along the transmission line. The Quartus II software
allows four settings for programmable pre-emphasis—zero (0), low (1), medium (2),
and high (3). The default setting is low.
The V_OD is also programmable with four settings: low (0), medium low (1), medium
high (2), and high (3). The default setting is medium low.
Programmable VOD
You can statically assign the V_OD settings from the Assignment Editor. Table 8–8 lists
the assignment name for programmable V_OD and its possible values in the Quartus II
software Assignment Editor.
Table 8–8. Quartus II Software Assignment Editor
To
tx_out
Assignment name
Allowed values
Programmable Differential Output Voltage (V_OD)
0, 1, 2, 3
Figure 8–10 shows the assignment of programmable V_OD for a transmit data output
from the Quartus II software Assignment Editor.
Figure 8–10. Quartus II Software Assignment Editor—Programmable V_OD
September 2012 Altera Corporation
Stratix IV Device Handbook
Volume 1