diff --git a/notes/USB.md b/notes/USB.md
index 607e216..3a13d9b 100644
--- a/notes/USB.md
+++ b/notes/USB.md
@@ -12,4 +12,12 @@ USB devices are one of the following:
 # Interconnects
 
 # Protocol
-A Universal Serial bus is strictly a *polled* bus, meaning the 
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+A Universal Serial bus is strictly a *polled* bus, meaning the host controller initiates every data transfer.
+
+Most bus transactions involve the transmission of up to three packets. 
+1. The token packet
+> Each transaction begins when the host, on a scheduled basis, sends a USB packet describing the type and direction of a transaction, the USB device address, and endpoint number.
+2. The data packet
+> Depending on the di
+3. The handshake packet
+> The destination, in general, responds to a handshake packet indicating whether the transfer was successful. 
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