Aside: Why programmable Output slew?
Slew rate is the measure of how fast an output can change value (measured in Volts/Sec).
Most FPGA vendors offer the capability of programming the output to be either fast slew or slow slew ----- WHY?
- Fast Slew rates cause more noise problems via ground bounce, especially when multiple outputs are switching
- If you have room in your timing spec, should use slow slew rate if possible