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→40pin UART test
# As can be seen from the table below, the uart available for Orange Pi 3B is uart3, uart7, and uart9. There are three sets of uart bus
::[[File:pi3b-img268-1.png]]
::{| class="wikitable" style="background-color:#ffffdc;width:800px;"
<big>'''As can be seen from the above table, i2c3_m0 and uart3_m0 are reused by pins, and the two cannot be opened at the same time'''</big>
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<ol start="2" style="list-style-type:decimal;"><li><p>In the linux system, the UART in the 40 pins is closed by default, and it needs to be opened manually before it can be used. The detailed steps are as follows:</p><ol style="list-style-type: lower-alpha;"><li><p>First run '''orangepi-config''', normal users remember to add sudo permission</p>{| class="wikitable" style="background-color:#ffffdc;width:800px;"
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<bigp>'''In the Linux system, the uart in 40pin is closed by default, and it needs to be opened manually to use.'''</big> '''Add the configuration of the red font part below to the /boot/orangepiEnv.txt, and then restart the Linux system to open the uart3, uart7, and uart9 at the same time. If you only need to open one, you can fill in one..''' orangepi@orangepi:~$ '''sudo vim /boot/orangepiEnv.txt''' orangepi-config'''<span style="color:#FF0000">overlays=uart3-m0 uart7-m2 uart9-m2</spanp>'''
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</li>
<li><p>Then select '''System'''</p>
<p>[[File:pi3b-1.png]]</p>
</li>
<li><p>Then select '''Hardware'''</p>
<p>[[File:pi3b-2.png]]</p>
</li>
<li><p>Then use the arrow keys on the keyboard to navigate to the position shown in the figure below, and then use the '''space''' to select the UART configuration you want to open</p>
<p>[[File:pi3b-3-3.png]]</p>
</li>
<li><p>Then select '''<Save>''' to save</p>
<p>[[File:pi3b-4.png]]</p>
</li>
<li><p>Then select '''<Back>'''</p>
<p>[[File:pi3b-5.png]]</p>
</li>
<li><p>Then select '''<Reboot>''' to restart the system to make the configuration take effect</p>
<p>[[File:pi3b-6.png]]</p>
</li>
</ol>
</li></ol>
<ol start="23" style="list-style-type: decimal;">
<li>After entering the Linux system, first confirm whether there is a device node corresponding to uart under/dev</li>
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</ol>
<ol start="34" style="list-style-type: decimal;">
<li>Then start testing the uart interface, first use the rx and tx of the uart interface to be tested by DuPont</li>
|Corresponding to the 27 pin
|Corresponding to the 15 pin
|Corresponding to the 7 22 pin
|}
[[File:pi3b-img269-1.png]]
</ol>
<ol start="45" style="list-style-type: decimal;">
<li><p>Use the '''gpio serial''' command to test the loop function of the serial port as shown below. If you can see the following printing, it means that the serial communication is normal</p>
<ol style="list-style-type: lower-alpha;">
