docs/esp32: Add documentation for esp32.PCNT.

Document the new `esp32.PCNT` class for hardware pulse counting.

Originally authored by: Jonathan Hogg <me@jonathanhogg.com>

Signed-off-by: Jim Mussared <jim.mussared@gmail.com>

1 files changed, 21 insertions, 0 deletions

diff --git a/docs/esp32/quickref.rst b/docs/esp32/quickref.rst
index 49f546a17..7127cc402 100644
--- a/docs/esp32/quickref.rst
+++ b/docs/esp32/quickref.rst
@@ -566,6 +566,27 @@ ESP32 S2:
 
     Provided to deinit the adc driver.
 
+Pulse Counter (pin pulse/edge counting)
+---------------------------------------
+
+The ESP32 provides up to 8 pulse counter peripherals depending on the hardware,
+with id 0..7. These can be configured to count rising and/or falling edges on
+any input pin.
+
+Use the :ref:`esp32.PCNT <esp32.PCNT>` class::
+
+    from machine import Pin
+    from esp32 import PCNT
+
+    counter = PCNT(0, pin=Pin(2), rising=PCNT.INCREMENT)        # create counter
+    counter.start()                                             # start counter
+    count = counter.value()                                     # read count, -32768..32767
+    counter.value(0)                                            # reset counter
+    count = counter.value(0)                                    # read and reset
+
+The PCNT hardware supports monitoring multiple pins in a single unit to
+implement quadrature decoding or up/down signal counters.
+
 Software SPI bus
 ----------------