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.. _usart:
=======
USART
=======
.. contents::
:local:
Hardware/Circuit Design
-----------------------
The Maple has 3 separate USART devices: ``Serial1``, ``Serial2``, and
``Serial3``. In the most simple use case, the RX and TX pins are used
to send data at a predetermined baudrate with the line voltage level
relative to ground.
+-----------+--------+-----+
|Port |Function|Pin |
+===========+========+=====+
|``Serial1``|TX |D7 |
| | | |
| |RX |D8 |
| | | |
| |CK |D6 |
+-----------+--------+-----+
|``Serial2``|TX |D1 |
| | | |
| |RX |D0 |
| | | |
| |CK |D10 |
| | | |
| |CTS |D2 |
| | | |
| |RTS |D3 |
+-----------+--------+-----+
|``Serial3``|TX |D29 |
| | | |
| |RX |D30 |
| | | |
| |CK |D31 |
| | | |
| |CTS |D32 |
| | | |
| |RTS |D33 |
+-----------+--------+-----+
.. TODO make above less ugly
Compatible Devices and Specifications
-------------------------------------
We have successfully used the Maple USART ports with an FT232R-based USB-serial converter at up to 115200 baud; higher speeds should certainly be possible.
Function Reference
------------------
In the following, you may replace ``SerialN`` with ``Serial1``,
``Serial2``, or ``Serial3``.
``SerialN.begin(baudrate)``
``SerialN.begin`` is usually called in `setup()`_ to configure the
baudrate of the given serial port and to set up the header pins
appropriately. It can be called at any time to reconfigure a port
or to change the baudrate. 9600 baud is the generic speed most
widely supported by other devices and terminals.
``SerialN.print(...)``/\ ``SerialN.println(...)``
Writes data into the port buffer to be transmitted as soon as
possible. Accepts strings (``char*``). If a raw integer is
passed, the corresponding ASCII character will be transmitted; to
print out a number in human readable form add a second parameter
with the base system.
For example, to print out the decimal number '1234' use
``SerialN.print(1234, DEC)``; to print out the binary number
'1001', use ``SerialN.print(9, BIN)``.
``SerialN.available()``/\ ``SerialN.read()``
``SerialN.read()`` will return the next unread character that has
been received over the port. ``SerialN.available()`` returns how
many such bytes are available (or zero if none are). If none are
available, ``SerialN.read()`` will block/fail, so the usual
program structure is to poll with ``SerialN.available`` and only
read if a nonzero value is returned.
Recommended Reading
-------------------
* `Wikipedia article on Universal asynchronous receiver/transmitter (USART) <http://en.wikipedia.org/wiki/Universal_asynchronous_receiver/transmitter>`_
* `Arduino reference on Serial <http://arduino.cc/en/Reference/Serial>`_
* STMicro documentation for STM32F103RB microcontroller:
* `All <stm32-all>`_
* `Datasheet <datasheet>`_ (pdf)
* `Reference Manual <full-manual>`_ (pdf)
|
