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+.. _usb-doc:
+
+================================================================================
+USB
+================================================================================
+
+This page documents the low level USB configuration. 
+If you're looking for a higher level protocol documentation see :ref:`Native Protocol <native-protocol>` and :ref:`ASCII Protocol <ascii-protocol>`.
+
+This page assumes that you are familiar with the general USB architecture, in particular with terms like "configuration", "interface" and "endpoint".
+
+On USB the ODrive provides a single configuration which is a composite device consisting of a CDC device (virtual COM port) and a vendor specific device.
+
+.. dropdown:: What is a composite device?
+
+    A composite device is a device where interfaces are grouped by interface association descriptors. 
+    For such devices, the host OS loads an intermediate driver, so that each of the interface groups can be treated like a separate device and have its own host-side driver attached.
+
+
+The following interface groups are present:
+
+ * Interface Association: Communication Device Class (CDC)
+    * Interface 0:
+        * Endpoint `0x82`: CDC commands
+
+    * Interface 1:
+        * Endpoint `0x01`: CDC data OUT
+        * Endpoint `0x81`: CDC data IN
+
+ * Interface Association: Vendor Specific Device Class
+    * Interface 2:
+        * Endpoint `0x03`: data OUT
+        * Endpoint `0x83`: data IN
+
+The CDC interface (endpoint pair `0x01, 0x81`) runs the :ref:`ASCII Protocol <ascii-protocol>` by default (see :code:`odrv0.config.enable_ascii_protocol_on_usb`). 
+The vendor specific interface (endpoint pair `0x03, 0x83`) runs the :ref:`Native Protocol <native-protocol>` (the packet based variant).
+
+The two interfaces can not (yet) be used simultaneously.