Sigma DE2-70 manual Using the LEDs and Switches, Switch debouncing

DE2-70 User Manual

position and then reset the board by turning the power switch off and back on; this action causes the new configuration data in the EPCS16 device to be loaded into the FPGA chip.

USB Blaster Circuit

Quartus II	USB		PROG/RUN
		MAX
Programmer		3128
AS Mode			"PROG"

AS Mode

Config

Auto	JTAG Config Port
Power-on Config

EPCS16

Serial

Configuration

Device

Figure 5.2. The AS configuration scheme.

In addition to its use for JTAG and AS programming, the USB Blaster port on the DE2-70 board can also be used to control some of the board's features remotely from a host computer. Details that describe this method of using the USB Blaster port are given in Chapter 3.

5.2 Using the LEDs and Switches

The DE2-70 board provides four pushbutton switches. Each of these switches is debounced using a Schmitt Trigger circuit, as indicated in Figure 5.3. The four outputs called KEY0, KEY1, KEY2, and KEY3 of the Schmitt Trigger devices 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 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.

Figure 5.3. Switch debouncing.

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