Cmod A7 Reference Manual

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Figure 5.1. Cmod A7 Quad-SPI Flash.

6

Basic I/O

The Cmod A7 includes a tri-color LED, two push buttons, and two individual LEDs. The push buttons are connected

to the FPGA via series resistors to prevent damage from inadvertent short circuits (a short circuit could occur if an

FPGA pin assigned to a push button was inadvertently defined as an output). The two push buttons are momentary

switches that normally generate a low output when they are at rest, and a high output only when they are

pressed.

Figure 6.1. Cmod A7 Basic I/O.

The two individual high-efficiency LEDs are anode-connected to the FPGA via 330-ohm resistors, so they will turn

on when a logic high voltage is applied to their respective I/O pin. Additional LEDs that are not user-accessible

indicate power-on, FPGA programming status, and USB-UART traffic.

6.1

Tri-color LED

The Cmod A7 contains a tri-color LED. The tri-color LED has three smaller internal LEDs: one red, one blue, and one

green. The anodes of these LEDs are connected to the 3.3V rail, and the cathodes are connected to FPGA signals.

Driving one of the RGB LED signals connected to the FPGA low will cause current to flow through the

corresponding LED, illuminating it. The tri-color LED will emit a color dependent on the combination of internal

LEDs that are currently being illuminated. For example, if the red and blue signals are driven low and green is

driven high, the tri-color LED will emit a purple color.

Note: Digilent strongly recommends the use of pulse-width modulation (PWM) when driving the tri-color LED.

Driving any of the inputs to a steady logic ‘1’ will result in the LED being illuminated at an uncomfortably bright

level. You can avoid this by ensuring that none of the tri-color signals are driven with more than 50% duty cycle.

Using PWM also greatly expands the potential color palette of the tri-color LED. Individually adjusting the duty