How do I add a probe to my design?
1. Launch FPGA Editor, either by means of the command line (fpga_editor) or the GUI (ISE).
2. Load the design's NCD file, either MAP (map.ncd) or PAR (design.ncd), and select the Edit Mode to be "Read Write" (File ->
Main Properties -> Edit Mode: Read Write).
3. Select "Tools" -> "Probes" from the menu.
4. Select the "Add" button to add a probe.
5. Select "Pin Name" (optional).
6. In the "Select Net" box, highlight the net that you wish to probe.
7. Choose the "Method" (either Automatic or Manual) in the "Select Pin Numbers" box. ("Automatic" picks the closest pin to the net to be probed. "Manual" allows you to choose which pin is used for the probe.)
8. Press the "OK" button to add the probe.
9. The probe is now listed in the "Probes" window along with the delay and the pin number.