Spartan-3A/3AN FPGA Starter Kit Board User Guidewww.xilinx.com 27UG334 (v1.1) June 19, 2008Push-Button SwitchesRPush-Button SwitchesLocations and LabelsThe Spartan-3A/3AN Starter Kit board has four momentary-contact push-buttonswitches, shown in Figure 2-5. The push buttons are located in the lower right corner of theboard and are labeled BTN_NORTH, BTN_EAST, BTN_SOUTH, and BTN_WEST. TheFPGA pins that connect to the push buttons appear in parentheses in Figure 2-5, and theassociated UCF is listed in Figure 2-7.OperationPressing a push button connects the associated FPGA pin to 3.3V, as shown in Figure 2-6.Use an internal pull-down resistor within the FPGA pin to generate a logic Low when thebutton is not pressed. Figure 2-7 shows how to specify a pull-down resistor within theUCF. There is no active debouncing circuitry on the push button.Figure 2-5: Four Push-Button Switches Surround the Rotary Push-Button SwitchUG334_c2_05_052407BTN_WEST(U15)BTN_EAST(T16)ROT_A: (T13)ROT_B: (R14)ROT_CENTER: (R13)BTN_NORTH(T14)BTN_SOUTH(T15)Requires an internal pull-upRequires an internal pull-upRequires an internal pull-downRotary Push Button SwitchNotes:1. All BTN_* push-button inputs require an internal pull-down resistor.Figure 2-6: Push-Button Switches Require an Internal Pull-Down Resistor in theFPGA Input PinUG230_c2_03_021206BTN_* SignalPush Button3.3V FPGA I/O Pin
