How do I adjust the slew rate for output signals?
The software default is to set all outputs to a FAST slew rate, but you can adjust this default in the fitter options. For individual control of output pins, you can specify the information in the User Constraints File (UCF) or by means of the Assign Package Pins process in ISE.
Example for UCF syntax:
NET mydataout FAST;
NET mydataout2 SLOW;
where "mydataout" or "mydataout2" are top-level ports in your design.
By default, all output slew rates are set to FAST, which corresponds to the Tout specification in the data sheet. If you designate an output as SLOW, you must add the Tslew delay to Tout.
Alternatively, in ABEL you can use:
XILINX PROPERTY 'FAST|SLOW [optional signal list]';