diff --git a/USB-config-%26-command-protocol.md b/USB-config-%26-command-protocol.md
index 4625bee..bfe1241 100644
--- a/USB-config-%26-command-protocol.md
+++ b/USB-config-%26-command-protocol.md
@@ -1,4 +1,5 @@
 # Wire protocol
+The device has a "configuration and command" USB *vendor* interface, typically at interface number 0 (depending on the mode), and endpoint number 1.
 
 The host sends a message and the device sends a reply. The device never initiates a transfer.