What does "B:" or "S:" represent in the following lines from a UCF file?
NET "input1" LOC = "S: PIN3";
NET "input2" LOC = "B: PIN4";
This was generated by the Xilinx design tools when I performed a "Lock Device Pins" process.
The usual syntax is:
NET "input1" LOC = P3;
I cannot find a reference to "S: PINnn" or "B: PINnn" (where nn stands for number) in the Libraries Guide.
These two options are generated by Pin2UCF for Xilinx CPLD families only.
"S:" is used before the pin locks to ensure that the CPLD fitter optimizes feedback the same way each time, and provides consistent timing results after subsequent re-fits.
"B:" is used before the pin locks to indicate that this signal is buffered and should remain so to ensure successful fitting for subsequent implementations.