Manual Pin Assignment Precautions

When you manually assign output and I/O pins, you force the fitter to place logic functions into specific function blocks. If the logic does not exceed the function block resources (macrocells, product terms and inputs) and the function block has the correct external pin resources to meet the logic I/O requirements, the logic is mapped into the function block and the design will route in the switch matrix.

Clocks

When preassigning rising or falling edge clocks to pins, assign them to the global GCK pins if you want to take advantage of global clock routing.

Output Enables

When preassigning active high or active low output enables to pins, assign them to global GTS pins if you want to take advantage of global tristate routing.

Set and Reset

When preassigning an active high or active low Set/Reset signal to a pin, assign it to the global GSR pin if you want to take advantage of global set/reset routing.