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→40pin UART test
<li><p>UART7 and UART9 are enabled by default in Android. The position of the 40pin is shown in the figure below, and the corresponding device nodes are '''/dev/ttyS7''' and '''/dev/ttyS9''' respectively</p>
<p>[[File:cm4-img452.png]]</p></li>
<li><p>First click on the wiringOP icon to open the wiringOP APP</p></li></ol>
[[File:cm4-img444.png]]
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<li>The main interface of wiringOP APP is displayed as shown in the figure below, and then click the '''UART_TEST''' button to open the UART test interface</li></ol>
[[File:cm4-img453.png]]
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<li>The serial port test interface of the APP is shown in the figure below</li></ol>
[[File:cm4-img454.png]]
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<li>Take the test of '''UART7''' as an example below, select the '''/dev/ttyS7''' node in the selection box, enter the baud rate you want to set in the edit box, and then click the '''OPEN''' button to open the /dev/ttyS7 node. After the opening is successful, the '''OPEN''' button becomes unselectable, and the '''CLOSE''' button and '''SEND''' button become selectable</li></ol>
[[File:cm4-img455.png]]
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<li>Then use Dupont wire to short the RXD and TXD pins of uart7</li></ol>
[[File:cm4-img456.png]]
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<li>Then you can enter a character in the send edit box below, and click the '''SEND''' button to start sending</li></ol>
[[File:cm4-img457.png]]
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<li>If everything is normal, the received string will be displayed in the receiving box</li></ol>
[[File:cm4-img458.png]]
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<span id="pin-spi-test-2"></span>
=== 40pin SPI test ===