diff --git a/doc/source/.vscode/settings.json b/doc/source/.vscode/settings.json
new file mode 100644
index 0000000..d5d660b
--- /dev/null
+++ b/doc/source/.vscode/settings.json
@@ -0,0 +1,3 @@
+{
+    "restructuredtext.confPath": "${workspaceFolder}"
+}
\ No newline at end of file
diff --git a/doc/source/hardware/hardware-watchdog.rst b/doc/source/hardware/hardware-watchdog.rst
new file mode 100644
index 0000000..dfa9f0b
--- /dev/null
+++ b/doc/source/hardware/hardware-watchdog.rst
@@ -0,0 +1,27 @@
+.. _hw_watchdog:
+
+Hardware Watchdog
+=================
+
+the PCB (> v1.3) is equipped with an external power supply monitor and hardware watchdog IC ``STM6822S``.
+The watchdog is periodically reset by the firmware.
+
+.. note:: The external watchdog is only activated in Release mode. When building the application in Debug mode, it is deactivated because setting breakpoints or other events that distrb the program flow would trigger a the external watchdog and force a software reset.
+
+
+During startup of the power supply, it keeps the controller in reset until the power supply is stable.
+The following picture shows the 3.3 Volt supply rail on channel 2 and the low active reset signal of the STM32F407 on channel 1.
+
+.. image:: hw_watchdog_delay.png
+    :alt: Image not found
+
+The total startup delay is larger than 200 ms.
+
+The follwoing figure shows the startup of the voltage rgulator and the reset signal.
+
+.. image:: hw_watchdog_startup.png
+    :alt: Image not found
+    
+The power supply is gradually ramped up over approximately 500 us. The external watchdog does not work fpr voltages below 0.9 Volt. Therefore the reset signal rises simultaneously.
+Once the supply voltage exceeds 0.9 Volts, the reset signal is pulled low. This ensures that the controller is not able to start until the > 200 ms startup time have passed.
+
diff --git a/doc/source/hardware/index.rst b/doc/source/hardware/index.rst
index b5ba6d2..d887cdf 100644
--- a/doc/source/hardware/index.rst
+++ b/doc/source/hardware/index.rst
@@ -3,7 +3,7 @@
 Hardware
 ========
 
-This guide on the reflow controller's hardware is based on the ``reflow-oven-control-pcb`` -- Version ``v1.2``
+This guide on the reflow controller's hardware is based on the ``reflow-oven-control-pcb`` -- Version ``v1.3``
 
 .. toctree::
 	:maxdepth: 2
diff --git a/doc/source/hardware/modifications.rst b/doc/source/hardware/modifications.rst
index 35a8c40..2935f80 100644
--- a/doc/source/hardware/modifications.rst
+++ b/doc/source/hardware/modifications.rst
@@ -1,7 +1,7 @@
-.. _hardware_modifications:
+.. _hardware_modifications_v1_2:
 
-Hardware Modifications
-======================
+Hardware Modifications for PCB v1.2
+===================================
 
 Analog Frontend
 ---------------
@@ -13,3 +13,11 @@ Power Supply
 ------------
 .. note::
 	Replace transformer ``BV-EI-303-2010`` with ``BV-EI-303-2050``, which has the same footprint but a little more power and does not heat that much.
+
+.. _hardware_modifications_v1_3:
+
+Hardware Modifications for PCB v1.3
+===================================
+
+.. note::
+	solder jumpers to bridge GND and Earth together must be soldered for the SD card slot to work properly. The card detect's switch terminal is on Earth potential.
\ No newline at end of file
diff --git a/doc/source/index.rst b/doc/source/index.rst
index 114eefb..591c963 100644
--- a/doc/source/index.rst
+++ b/doc/source/index.rst
@@ -10,7 +10,8 @@ Quick Links
 ===========
 
 * :ref:`genindex`
-* :ref:`hardware_modifications`
+* :ref:`hardware_modifications_v1_2`
+* :ref:`hardware_modifications_v1_3` 
 
 .. warning::
 	Although the Shimatta Reflow Controller provides a bunch of safety mechanisms that -- in theory -- prevent your house from burning down, NEVER leave the oven controller running unattended. This project is published in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.