One of the most useful techniques for debugging software is to print
messages to a terminal. The STM32 micro-controllers provide the necessary
capability for serial communications through USART (universal synchronous
asynchronous receiver transmitter) devices, but not the physical connection
necessary to communicate with a host computer. For the tutorials we utilize
a common USB/UART bridge. The most common of these are meant as serial
port replacements for PCs and are unsuitable for our purposes because
they include voltage level converters to satisfy the RS-232 specification. Instead
we require a device which provides more direct access to the pins of the
USB/UART bridge device.