docs/library: Add machine.DAC documentation.

Fixes issue #7915.

Signed-off-by: Matt Trentini <matt.trentini@gmail.com>

docs/library/machine.DAC.rst

@@ -0,0 +1,68 @@
+.. currentmodule:: machine
+.. _machine.DAC:
+
+class DAC -- digital to analog conversion
+=========================================
+
+The DAC is used to output an analog voltage based on a digital value.
+
+The output voltage will be between 0 and 3.3V.
+
+DAC is currently supported on ESP32 [#esp32_dac]_, SAMD and Renesas RA.
+
+.. note::
+  The STM32 port has similar functionality to ``machine.DAC``. See
+  :ref:`pyb.DAC <pyb.DAC>` for details.
+
+Example usage (ESP32)::
+
+    from machine import DAC
+
+    dac = DAC(pin)    # create a DAC object acting on a pin
+    dac.write(128)    # write a value to the DAC
+    dac.write(255)    # output maximum value, 3.3V
+
+Constructors
+------------
+
+.. class:: DAC(id)
+
+  Construct a new DAC object.
+
+  ``id`` is a pin object (ESP32 and Renesas RA) or an index to a DAC resource (SAMD).
+
+.. note::
+  On the ESP32, DAC functionality is available on pins 25 and 26. On the
+  ESP32-S2, pins 17 and 18. See :ref:`ESP32 Quickref <esp32_quickref>`
+  for more details.
+
+.. note::
+  SAMD21 has one DAC resource, SAMD51 has two. See :ref:`SAMD Quickref <samd_quickref>`
+  for more details.
+
+Methods
+-------
+
+.. method:: DAC.write(value)
+
+  Output an analog voltage to the pin connected to the DAC.
+
+  ``value`` is a representation of the desired output; a linear interpolation of
+  0-3.3V, though the range differs depending on the port and micro, see below:
+
+  +--------------+------+--------+
+  | *Port/micro* | Bits | Range  |
+  +==============+======+========+
+  | ESP32        | 8    | 0-255  |
+  +--------------+------+--------+
+  | SAMD21       | 10   | 0-1023 |
+  +--------------+------+--------+
+  | SAMD51       | 12   | 0-4095 |
+  +--------------+------+--------+
+  | Renesas RA   | 12   | 0-4095 |
+  +--------------+------+--------+
+
+.. rubric:: Footnotes
+
+.. [#esp32_dac] The original ESP32 and ESP32-S2 *only*, since DAC hardware is
+    not present on other microcontrollers in the family.

docs/library/machine.rst

@@ -260,6 +260,7 @@ Classes
    machine.Signal.rst
    machine.ADC.rst
    machine.ADCBlock.rst
+   machine.DAC.rst
    machine.PWM.rst
    machine.UART.rst
    machine.SPI.rst