Xilinx Spartan-3E - Push-Button Switches

16 www.xilinx.com Spartan-3E Starter Kit Board User Guide
UG230 (v1.0) March 9, 2006
Chapter 2: Switches, Buttons, and Knob
R
Push-Button Switches
Locations and Labels
The Spartan-3E Starter Kit board has four momentary-contact push-button switches,
shown in Figure 2-3. The push buttons are located in the lower left corner of the board and
are labeled BTN_NORTH, BTN_EAST, BTN_SOUTH, and BTN_WEST. The FPGA pins
that connect to the push buttons appear in parentheses in Figure 2-3 and the associated
UCF appears in Figure 2-5.
Operation
Pressing a push button connects the associated FPGA pin to 3.3V, as shown in Figure 2-4.
Use an internal pull-down resistor within the FPGA pin to generate a logic Low when the
button is not pressed. Figure 2-5 shows how to specify a pull-down resistor within the
UCF. There is no active debouncing circuitry on the push button.
Figure 2-2: UCF Constraints for Slide Switches
NET "SW<0>" LOC = "L13" | IOSTANDARD = LVTTL | PULLUP ;
NET "SW<1>" LOC = "L14" | IOSTANDARD = LVTTL |
PULLUP ;
NET "SW<2>" LOC = "H18" | IOSTANDARD = LVTTL |
PULLUP ;
NET "SW<3>" LOC = "N17" | IOSTANDARD = LVTTL |
PULLUP ;
Figure 2-3: Four Push-Button Switches Surround Rotary Push-Button Switch
UG230_c2_02_021206
BTN_WEST
(D18)
BTN_EAST
(H13)
ROT_A: (K18)
ROT_B: (G18)
ROT_CENTER: (V16)
BTN_NORTH
(V4)
BTN_SOUTH
(K17)
Requires an internal pull-up
Requires an internal pull-up
Requires an internal pull-down
Rotary Push Button Switch
Notes:
1. All BTN_* push-button inputs require an internal pull-down resistor.
2. BTN_SOUTH is also used as a soft reset in some FPGA applications.