The default slew displayed in the I/O Attribute Editor window is based on the I/O Standard.
The Slew cell indicates the slew rate for output buffers. Generally, available slew rates are high and low. For those devices that support additional slew values, Actel recommends that you use the high and low values and let the software map to the appropriate absolute slew value.
To set the slew rate:
Select CUSTOM (SX-A and RTSX-S) from the I/O Standard cell in the macro row to edit.
Select the slew rate (high or low) from the Slew cell.
Note: The slow slew rate is incompatible with 3.3V PCI requirements.