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Introduction
------------

All COM are delivered with pre-installed U‑Boot bootloader
firmware. U‑Boot supports several low-level-debugging options and file
download via Ethernet (TFTP), USB or via UART/serial
X/Y/Z-Modem. These files can additionally be stored into the permanent
flash-memory (NAND/eMMC) to be started by command or power-on.

Furthermore, the user can communicate with the bootloader via serial
console, provided via RS232 using a :ref:`software-documentation/uboot/terminal:Terminal Program`.

.. note::

   For full documentation, incl. comprehensive command reference of U‑Boot please refer to: `The U-Boot Documentation`_


To communicate with the CoM's bootloader users need to connect to it via RS232 serial port, which dependent on the
baseboard either is a D-SUB9 or pin-header (see :ref:`Baseboard Pinouts<baseboard-pinouts>`, or
:ref:`TTL Debug UART pin header<ttl-converter-connection>`) connector, where the latter requires a TTL-2-USB RS232 converter.


.. _`The U-Boot Documentation`: https://u-boot.readthedocs.io