26 www.xilinx.comSpartan-3A/3AN FPGA Starter Kit Board User GuideUG334 (v1.1) June 19, 2008Chapter 2: Switches, Buttons, and Rotary Knob RSUSPEND SwitchThe SUSPEND slide switch, shown in Figure 2-3, connects directly to the FPGA’sSUSPEND input pin. If Suspend mode is enabled in the FPGA application, then the FPGAenters Suspend mode whenever the switch is set to “SUSPEND.” If the switch is thenchanged back to “RUN,” then the FPGA resumes operation from the state before it enteredSuspend mode. Likewise, if Suspend mode is enabled, then the AWAKE pin is reserved toindicate when the FPGA is in Suspend mode. See “AWAKE LED,” page 32.To enable Suspend mode, add the configuration string shown in Figure 2-4 to the userconstraints file (UCF). If Suspend mode is not enabled in the application, then theSUSPEND switch has no affect on the design and the AWAKE pin is available as a general-purpose I/O.For more information on Suspend mode, see the following application note:• XAPP480: Using Suspend Mode in Spartan-3 Generation FPGAswww.xilinx.com/support/documentation/application_notes/xapp480.pdfFigure 2-2: UCF Constraints for Slide SwitchesNET "SW<0>" LOC = "V8" | IOSTANDARD = LVCMOS33 ;NET "SW<1>" LOC = "U10"| IOSTANDARD = LVCMOS33 ;NET "SW<2>" LOC = "U8" | IOSTANDARD = LVCMOS33 ;NET "SW<3>" LOC = "T9" | IOSTANDARD = LVCMOS33 ;Figure 2-3: Suspend SwitchFigure 2-4: UCF Constraints to Enable Suspend ModeUG334_c2_03_052407SUSPENDRUNCONFIG ENABLE_SUSPEND = “FILTERED” ;
