User manual

Zybo Z7 Board Reference Manual

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green. Driving the signal corresponding to one of these colors high will illuminate the internal LED. The input

signals are driven by the Zynq PL through a transistor, which inverts the signals. Therefore, to light up the tri-

color LED, the corresponding signals need to be driven high. 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 high and green is driven low, 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 LEDs.

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 a 50% duty cycle.

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

cycle of each color between 50% and 0% causes the different colors to be illuminated at different intensities,

allowing virtually any color to be displayed.

14 Fan

The Zybo Z7-20 has a connector that can be used to power a fan mounted to the included heat sink. In order to

attach the fan to the Zybo Z7-20 heat sink, two of the included screws must be tightened into the space between

the heat sink fins (the heat sink does not contain mounting holes). The fan must be attached with the label facing

down, towards the Zynq device, in order to push the air flow in the correct direction. After mounting the fan, plug

the fan into the 3-pin fan connector (J14) on the Zybo Z7-20 to use it. A Zybo Z7-20 with the fan properly attached

is shown in Fig. 14.1.

Figure 14.1. Zybo Z7-20 with Fan.

Once the fan has been installed and connected, it will always be on when the Zybo Z7-20 is turned on. It is possible

to monitor the speed of the fan using the “FAN_FB_PU” signal, which is connected to the feedback signal of the

fan. This generates a pulse with a frequency proportional to the rotation speed of the fan. Each rotation generates

two pulses. The period of these pulses shortens with higher rotation speed and lengthens at slower speeds. If the

fan speed feedback signal is held at logic high or logic low and is not changing then the fan is locked and is not

spinning. The behavior of the fan speed feedback signal is shown in Fig. 14.2.