update

更新免开发文档的内容和协议文档

en/docs/dev_doc/protocols/xu316_zerocode_protocol.md

@@ -225,6 +225,7 @@ sequenceDiagram
     | 0x24 | XU316 send playback volume | XU316→MCU |
     | 0x25 | Send recording volume | XU316→MCU |
     | 0x26 | Switch MCLK | MCU→XU316 |
+    | 0x29 | Report USB connection status | XU316→MCU |
 
 === "HID-MCU Passthrough Commands (0xEE-0xEF)"
     | Command | Command Description | Direction |
@@ -745,7 +746,37 @@ sequenceDiagram
 === "Function Description"
     - Send audio format time delay
 
-#### 3.3.10 Get Firmware Version Command (0xF1)
+#### 3.3.10 Report USB Connection Status (0x29)
+
+=== "Command Format"
+    **XU316 Sends**
+    ```
+    Frame Header:  2 bytes - 0x55aa
+    Version:       1 byte  - 0x00
+    Command:       1 byte  - 0x29
+    Data Length:   1 byte  - 0x01 (1 byte)
+    Data:          1 byte  - USB connection status
+                               0x00 USB disconnected / not connected
+                               0x01 USB connected
+    Checksum:      1 byte  - Sum of all bytes from frame header, modulo 256
+    ```
+
+    **MCU Returns**
+    ```
+    Frame Header:  2 bytes - 0x55aa
+    Version:       1 byte  - 0x03
+    Command:       1 byte  - 0x29
+    Data Length:   1 byte  - 0x00
+    Data:          0 bytes
+    Checksum:      1 byte  - Sum of all bytes from frame header, modulo 256
+    ```
+
+=== "Function Description"
+    - This command is used by XU316 to report the current USB connection status to the MCU
+    - When the USB connection status changes (connect or disconnect), XU316 proactively sends this command
+    - The MCU can use this information to update the UI or adjust related functions
+
+#### 3.3.11 Get Firmware Version Command (0xF1)
 
 === "Command Format"
     **MCU Sends**