Why isn't slow slew rate control an available logic option for Stratix® II and Cyclone® II devices?

The slow slew rate logic option on previous device families manipulated drive strength settings to achieve different edge rates on the output buffers. Stratix®  II and Cyclone®  II devices offer more drive strength settings per I/O standard. Slew rate can be changed by using different drive strength settings. Fast edge rates can be
achieved with larger current settings, slower rates can be achieved with lower current settings. Use the device family's IBIS models to determine actual edge rates for each drive strength setting per I/O standard.

IBIS models for Altera® devices can be downloaded at www.altera.com.