Spartan-3E Starter Kit Board User Guide www.xilinx.com 19UG230 (v1.0) March 9, 2006Discrete LEDsRdirection! See the Rotary Encoder Interface reference design in“Related Resources” for anexample.UCF Location ConstraintsFigure 2-9 provides the UCF constraints for the four push-button switches, including theI/O pin assignment and the I/O standard used, and defines a pull-down resistor on eachinput.Discrete LEDsLocations and LabelsThe Spartan-3E Starter Kit board has eight individual surface-mount LEDs located abovethe slide switches as shown in Figure 2-10. The LEDs are labeled LED7 through LED0.LED7 is the left-most LED, LED0 the right-most LED.Figure 2-8: Outputs from Rotary Shaft Encoder May Include Mechanical ChatterABDetentDetentUG230_c2_07_030606Rotating RIGHTSwitch closing chatter on ‘B’injects false “clicks” to the LEFT(’B’ rising edge when ‘A’ is Low)Switch opening chatter on ‘A’injects false “clicks” to the RIGHTRising edge on ‘A’ when ‘B’ is Low indicates RIGHT (clockwise) rotationFigure 2-9: UCF Constraints for Rotary Push-Button SwitchNET "ROT_A" LOC = "K18" | IOSTANDARD = LVTTL | PULLUP ;NET "ROT_B" LOC = "G18" | IOSTANDARD = LVTTL | PULLUP ;NET "ROT_CENTER" LOC = "V16" | IOSTANDARD = LVTTL | PULLDOWN ;Figure 2-10: Eight Discrete LEDsUG230_c2_04_021206LED7: (F9)LED6: (E9)LED5: (D11)LED4: (C11)LED3: (F11)LED2: (E11)LED1: (E12)LED0: (F12)
