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+.. _lang-board-values:
+
+Board-Specific Constants
+========================
+
+There are a number of board-specific values: constants or variables
+which are different depending on which LeafLabs board you have.
+
+This page lists and documents the board-specific values.  You should
+use these when appropriate in your own programs.  This will help make
+it easier to share your code with other people who have different
+boards.  Some example usages are given :ref:`below
+<lang-board-values-examples>`.
+
+.. contents:: Contents
+   :local:
+
+Constants
+---------
+
+- ``CYCLES_PER_MICROSECOND``: Number of CPU cycles per microsecond on
+  your board.
+
+.. _lang-board-values-but:
+
+- ``BOARD_BUTTON_PIN``: Pin connected to the built-in button (labeled
+  "BUT" on your board's silkscreen).
+
+.. _lang-board-values-led:
+
+- ``BOARD_LED_PIN``: Pin connected to the built-in LED.
+
+- ``BOARD_NR_GPIO_PINS``: Total number of :ref:`GPIO pins <gpio>` that
+  are broken out to headers.  Some of these might already be connected
+  to external hardware (like the built-in LED and button).  To find
+  out if a pin is in use, see :ref:`boardUsesPin()
+  <lang-boardusespin>` (and also :ref:`boardUsedPins
+  <lang-board-values-used-pins>`).
+
+.. _lang-board-values-nr-pwm-pins:
+
+- ``BOARD_NR_PWM_PINS``: Total *number* of GPIO pins that can be used
+  for :ref:`PWM <pwm>`.  The actual *pins* that can do PWM are in the
+  :ref:`boardPWMPins <lang-board-values-pwm-pins>` array.
+
+.. _lang-board-values-nr-adc-pins:
+
+- ``BOARD_NR_ADC_PINS``: Total number of GPIO pins that can be used
+  for :ref:`analog-to-digital conversion <adc>`.  The actual pins that
+  can do ADC conversion are in the :ref:`boardADCPins
+  <lang-board-values-adc-pins>` array.
+
+.. _lang-board-values-nr-used-pins:
+
+- ``BOARD_NR_USED_PINS``: Total number of GPIO pins that are already
+  connected to some external hardware (like a built-in LED) on the
+  board.  The actual pins that that are already used are in the
+  :ref:`boardUsedPins <lang-board-values-used-pins>` array.  To see if
+  a pin is already in use, use the :ref:`boardUsesPin()
+  <lang-boardusespin>` function.
+
+.. _lang-board-values-usart:
+
+- USART (serial port) related constants:
+
+    * ``BOARD_USART1_TX_PIN``, ``BOARD_USART2_TX_PIN``, ``BOARD_USART3_TX_PIN``:
+      TX pins for the 3 USARTS.
+
+    * ``BOARD_USART1_RX_PIN``, ``BOARD_USART2_RX_PIN``, ``BOARD_USART3_RX_PIN``:
+      RX pins for the 3 USARTS.
+
+    * ``BOARD_UART4_TX_PIN``, ``BOARD_UART5_TX_PIN``: TX pins for
+      UARTs 4 and 5 (high-density boards like Maple Native only).
+
+    * ``BOARD_UART4_RX_PIN``, ``BOARD_UART5_RX_PIN``: RX pins for
+      UARTs 4 and 5 (high-density boards like Maple Native only).
+
+    * ``BOARD_NR_USARTS``: Number of serial ports on the board.  This
+      number includes UARTs 4 and 5 if they are available.
+
+.. _lang-board-values-pwm-pins:
+.. _lang-board-values-adc-pins:
+.. _lang-board-values-used-pins:
+
+Pin Arrays
+----------
+
+Some :ref:`arrays <lang-array>` of pin numbers are available which you
+can use to find out certain important information about a given pin.
+
+.. TODO add links to the board-specific hardware information on what
+.. are in these arrays
+
+- ``boardPWMPins``: Pin numbers of each pin capable of :ref:`PWM
+  <pwm>` output, using :ref:`pwmWrite() <lang-pwmwrite>`.  The total
+  number of these pins is :ref:`BOARD_NR_PWM_PINS
+  <lang-board-values-nr-pwm-pins>`.
+
+- ``boardADCPins``: Pin numbers of each pin capable of :ref:`ADC
+  <adc>` conversion, using :ref:`analogRead() <lang-analogread>`.  The
+  total number of these pins is :ref:`BOARD_NR_ADC_PINS
+  <lang-board-values-nr-adc-pins>`.
+
+- ``boardUsedPins``: Pin numbers of each pin that, by default, is used
+  for some special purpose by the board.  The total number of these
+  pins is :ref:`BOARD_NR_USED_PINS <lang-board-values-nr-used-pins>`.
+  To check if a pin is used for a special purpose, use
+  :ref:`boardUsesPin() <lang-boardusespin>`.
+
+.. _lang-board-values-examples:
+
+Examples
+--------
+
+:ref:`BOARD_LED_PIN <lang-board-values-led>` On the Maple, the
+built-in LED is connected to pin 13.  On the Maple Mini, however, it
+is connected to pin 33.  You can write a "blinky" program that works
+on all LeafLabs boards using ``BOARD_LED_PIN`` and :ref:`toggleLED()
+<lang-toggleled>`::
+
+    void setup() {
+        pinMode(BOARD_LED_PIN, OUTPUT);
+    }
+
+    void loop() {
+        toggleLED();
+        delay(100);
+    }
+
+:ref:`BOARD_BUTTON_PIN <lang-board-values-but>`: Similarly, you can
+write a single program that prints a message whenever the button is
+pressed which will work on all LeafLabs boards using
+``BOARD_BUTTON_PIN`` and :ref:`isButtonPressed()
+<lang-isbuttonpressed>`::
+
+    void setup() {
+        pinMode(BOARD_BUTTON_PIN, INPUT);
+    }
+
+    void loop() {
+        if (isButtonPressed()) {
+            SerialUSB.println("You pressed the button!");
+        }
+    }
+
+See Also
+--------
+
+- :ref:`lang-boardusespin`
+- :ref:`lang-isbuttonpressed`
+- :ref:`lang-waitforbuttonpress`
+- :ref:`lang-pinmode`
+- :ref:`lang-toggleled`
+- :ref:`lang-analogread`
+- :ref:`lang-pwmwrite`