LEDs and Switches

Posted on Feb 5, 2014

The DE2 board provides four pushbutton switches. Each of these switches is debounced using a Schmitt Trigger circuit, as indicated in Figure 1. The four outputs called KEY0, . , KEY3 of the Schmitt Trigger device are connected directly to the Cyclone II FPGA. Each switch provides a high logic level (3. 3 volts) when it is not pressed, and provides a

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low logic level (0 volts) when depressed. Since the pushbutton switches are debounced, they are appropriate for use as clock or reset inputs in a circuit. There are also 18 toggle switches (sliders) on the DE2 board. These switches are not debounced, and are intended for use as level-sensitive data inputs to a circuit. Each switch is connected directly to a pin on the Cyclone II FPGA. When a switch is in the DOWN position (closest to the edge of the board) it provides a low logic level (0 volts) to the FPGA, and when the switch is in the UP position it provides a high logic level (3. 3 volts). There are 27 user-controllable LEDs on the DE2 board. Eighteen red LEDs are situated above the 18 toggle switches, and eight green LEDs are found above the pushbutton switches (the 9th green LED is in the middle of the 7-segment displays). Each LED is driven directly by a pin on the Cyclone II FPGA; driving its associated pin to a high logic level turns the LED on, and driving the pin low turns it off. A schematic diagram that shows the pushbutton and toggle switches is given in Figure 2. A schematic diagram that shows the LED circuitry appears in Figure 3.

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