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diff --git a/docs/en/unit/extio.md b/docs/en/unit/extio.md
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--- a/docs/en/unit/extio.md
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@@ -50,6 +50,13 @@ It’s difficult to foresee the needs of your project from the start. EXT.IO is
  <tr><td>EXT.IO Unit</td><td>SCL</td><td>SDA</td><td>5V</td><td>GND</td></tr>
 </table>
 
+## Schematic
+
+With reference to the schematic diagram and the PCA9554PW data sheet, the Unit can modify the I2C address of the device by controlling the level combination of the A0~A2 pins. (The default address is 0x27, please check the datasheet for more information)
+There are three chip resistance welding positions reserved on the PCB of the Unit, which are A0-A2 (R6-R8), as shown in the following figure.
+
+<img src="assets\img\product_pics\unit\extio\extio_sch.webp">
+
 ## Example
 
 ### 1. Arduino IDE
diff --git a/docs/zh_CN/unit/extio.md b/docs/zh_CN/unit/extio.md
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@@ -15,6 +15,7 @@
 - GROVE 接口, 支持 [UIFlow](http://flow.m5stack.com) 、 [Arduino](http://www.arduino.cc).
 - 2x LEGO 兼容孔
 
+
 ## 包含
 
 - 1x EXT.IO Unit
@@ -72,6 +73,14 @@
  <tr><td>EXT.IO Unit</td><td>SCL</td><td>SDA</td><td>5V</td><td>GND</td></tr>
 </table>
 
+
+## 原理图
+
+参考原理图及PCA9554PW数据手册可知，该Unit能够通过控制A0~A2引脚的电平组合，修改设备的I2C地址。(默认地址为0x27，更多信息请查看datasheet)
+在Unit的PCB板上预留了三个贴片电阻焊接位，分别为A0-A2(R6-R8)，如下图所示。
+
+<img src="assets\img\product_pics\unit\extio\extio_sch.webp">
+
 ## 相关链接
 
 - Datasheet - **[PCA9554PW](https://m5stack.oss-cn-shenzhen.aliyuncs.com/resource/docs/datasheet/unit/PCA9554PW_en.pdf)**