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OEM Integration Guide
Product Manuals - http://www.vescent.com/manuals/
used by a connected system to determine whether it is safe to allow signalling on the USART lines. If a
level-shifter or isolator is to be used in the system, it is recommended to use this 3.3V rail to power
the side connected to the master controller to prevent any signalling to go through to the master
controller when it is unpowered.
If no level-shifting or isolation is desired, then it is
recommended for the OEM integrator to use 1kΩ series
resistors on all USART communication lines going into the
master controller. These series resistors will protect the
microcontroller from over-voltages up to 3.3V while it is
unpowered.
USB to Serial Conversion
For ease of communication from a PC, it may be desirable to use a USART to USB converter. A
commonly used IC to do this is an
. This FTDI chip connects to the 3.3V UART interface and
then creates a virtual COM port on the PC connected to it. Standard methods of interacting with serial
ports may then be used for sending commands to the ICE-MC1 master controller. The FTDI chip has
an onboard 3.3V regulator and can be configured to signal at 3.3V on the serial UART lines. In
accordance with the UART protection recommendations given above, the 3.3V power rail provided
from the master controller can be used to power the FTDI chip's UART signalling pins, thereby
preventing any damage from occurring by signalling into an unpowered microcontroller on the master
controller. If this technique isn't used, series resistors should be used on the UART lines.
Sometimes the PC communicating with the ICE modules may be located far away or on a different
power circuit in the building. In this case, it may be desirable to isolate the power and ground of the
PC (via the USB cable) by using an galvanic isolator. The easiest place to put this isolator is between
the FTDI chip and UART of the master controller. The master controller's 3.3V rail can be used to
power one side of the isolator and the USB 5V rail can be used to power the other. The
uses an
to do this. An example implementation of this is shown
.
Fig. 15: Example implementation of USB isolation using ADUM7441
