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+.. _usart:
+
+USART
+=====
+
+A USART is more commonly known a *serial port*.  It's used to transmit
+information between Maple and another device (like your computer,
+another Maple, etc.).
+
+.. contents:: Contents
+   :local:
+
+.. _usart-circuit:
+
+Hardware/Circuit Design
+-----------------------
+
+To use a serial port to communicate with an external serial device,
+connect the TX pin to your device's RX pin, the RX to your device's TX
+pin, and your Maple board's ground to your device's ground.
+
+.. warning:: Don't connect these pins directly to an RS232 serial
+   port; they operate at +/- 12V and can damage your board.
+
+Each LeafLabs board has at least 3 separate USART devices. In the most
+simple use case, the RX and TX pins are used to send data at a
+predetermined speed (or *baud rate*).  Their usage is documented in
+the :ref:`Serial Ports <lang-serial>` language reference page.
+
+Which pins correspond to the USART TX and RX pins are given on your
+board's silkscreen, and also in the board-specific USART pin maps
+available here:
+
+* :ref:`Maple <maple-usart-map>`
+* :ref:`Maple RET6 Edition <maple-ret6-usart-map>`
+* :ref:`Maple Mini <maple-mini-usart-map>`
+* :ref:`Maple Native Beta <maple-native-b-usart-map>`
+
+If you use a particular serial port, you cannot also use its
+communication pins for other purposes at the same time.
+
+Compatible Devices and Specifications
+-------------------------------------
+
+We have successfully used the USART ports with an FT232R-based
+USB-serial converter at up to 115200 baud.  Higher speeds should
+certainly be possible.
+
+Recommended Reading
+-------------------
+
+* `Wikipedia article on Universal Asynchronous Receiver/Transmitter
+  (USART)
+  <http://en.wikipedia.org/wiki/Universal_asynchronous_receiver/transmitter>`_
+* `Arduino Serial reference
+  <http://arduino.cc/en/Reference/Serial>`_
+* ST `Reference Manual RM0008
+  <http://www.st.com/web/en/resource/technical/document/reference_manual/CD00171190.pdf>`_
+  (PDF), Chapter 27.
+* `Serial and UART Tutorial
+  <http://www.freebsd.org/doc/en/articles/serial-uart/>`_ (written for
+  FreeBSD, but contains a large amount of general information).