The default output capacitance appears in the Loading (pf) column of the I/O Attribute Editor. This default value is based upon the I/O specification set in the I/O Standard cell. If necessary, you can change the output capacitance default setting to improve timing definition and analysis. Both the capacitive loading on the board and the Vil/Vih trip points of driven devices affect output-propagation delay.
The I/O Attribute Editor provides a mechanism for setting the expected capacitance to improve the propagation-delay model. Timer, Timing-Driven Layout, Timing Report, and Back-Annotation will automatically use the modified delay model for delay calculations.
To specify capacitance:
Select CUSTOM from the I/O Standard cell in the desired macro row.
Set capacitance in the Loading (pf) column. You can modify the capacitance value to any integer value that accurately reflects the capacitive loading on the Actel device pins. Increasing capacitance will increase propagation delays.