::[[File:cm4-img444.png]]

<li>The main interface of wiringOP APP is displayed as shown in the figure below, and then click the '''GPIO_TEST''' button to open the GPIO test interface</li></ol>

<li>The GPIO test interface is shown in the figure below. The two rows of '''CheckBox''' buttons on the left are in one-to-one correspondence with the 40pin pins. When the '''CheckBox''' button is checked, the corresponding GPIO pin will be set to '''OUT''' mode, and the pin level will be set to high level; when the checkbox is unchecked, the GPIO pin level will be set to low level; When the '''GPIO READALL''' button is pressed, information such as wPi number, GPIO mode, and pin level can be obtained; when the '''BLINK ALL GPIO''' button is clicked, the program will control the 28 GPIO ports to continuously switch between high and low levels</li></ol>

<li>Then click the '''GPIO READALL''' button, the output information is as shown in the figure below:</li></ol>

<li>There are a total of 28 GPIO ports in the 40pins of the development board that can be used. The following uses pin 7—the corresponding GPIO is GPIO4_A4—the corresponding wPi serial number is 2—as an example to demonstrate how to set the high and low levels of the GPIO port. First click the '''CheckBox''' button corresponding to pin 7. When the button is selected, pin 7 will be set to high level. After setting, you can use a multimeter to measure the voltage value of the pin. If it is 3.3v, it means setting high level success</li></ol>

<li>Then click the '''GPIO READALL''' button, you can see that the current pin 7 mode is '''OUT''', and the pin level is high</li></ol>

<li>Click the '''CheckBox''' button in the figure below again to cancel the check status. Pin 7 will be set to low level. After setting, you can use a multimeter to measure the voltage value of the pin. If it is '''0v''', it means that the low level is set successfully.</li></ol>