THE DESIGN CYCLE
hardware will allow us to perform the same tasks we just
discussed using a drop-in USB interface.
The CP2103 is designed to transition a piece of
hardware from an RS-232/485 interface to a USB
interface. I was attracted to the CP2103 because of its
skinny schematic diagram. If I believe what the CP2103
datasheet schematic is telling me, it doesn't require any
external resistors or crystals to bring a fully compliant USB
2.0 interface to life. The silicon encapsulates a level 2.0
full-speed function controller, transceiver, EEPROM,
oscillator, and UART in a tiny QFN- 28 package. The
internal EEPROM is used for storing vendor-specific
information in commercial applications. If we find that
we need to access the EEPROM, there is easy access and
programming via its USB interface.
Silicon Laboratories has taken care of the PC side of
things by supplying royalty-free Virtual COM Port (VCP)
device drivers. If you've ever used a PC RS-232-to-USB
converter, you know that it looks like a standard COM
port to the PC and its applications. The VCP device
driver also pretends to be a
standard COM port. That means
that we can use our newly
acquired microcontroller USB
interface to communicate with a
Tera Term Pro terminal window
on a computer just as if we were
using RS-232 hardware on the
In many of the projects we've
done in Design Cycle, industry
standard regulated power supply
circuitry was eliminated and
replaced by regulated wall warts.
Including the CP2103 in our future
designs will allow us to totally
eliminate the wall warts, as well.
As long as our embedded microcontroller designs don't draw more
than 500 mA of current, we can
power them directly from the USB
connection. The CP2103 can also
■ PHOTO 2. This is the long way around as the WLAN
Phoenix has its own SP3232 RS-232 converter IC.
The idea is to use a CP2103 to get rid of both of the
RS-232 converters in this shot.
accommodate a 3. 3 volt microcontroller system as its
on-chip 3. 3 VDC voltage regulator can supply up to
100 mA to external circuitry.
Let's talk about the functional blocks that make up
the CP2103 beginning with the USB function controller
and transceiver. Basically, the USB function controller
manages all of the data transfers between the UART and
USB interfaces. The USB function controller is also
responsible for handling command requests that are
generated by the USB host controller. The CP2103's
internal UART is also under the command of the USB
function controller. The CP2103's USB 2.0-compliant
transceiver's functionality is rather obvious. The
transceiver's only reason to live is to send and receive
serial data on the USB bus.
There's nothing remarkable about the CP2103's UART
interface. If you think about all that has been said about
how the CP2103 can replace an
SP233ACP, it would make sense
that the UART does everything
exactly like any other UART would.
But in fact, it is much more
sophisticated than what is found
on many UART-equipped
microcontrollers. In addition to the
standard TXD and RXD (transmit
and receive) signals, the CP2103's
UART interface includes all of the
standard EIA modem signals.
For those of you that are too
young to remember dial-up BBSs
and watching modem LEDs
blinking late into the night, the
■ PHOTO 3. Only seven
inexpensive components and
a USB connector are needed to
put a CP2103-based USB interface
to work. These components are
mounted on the CP2103 Evaluation
Kit printed circuit board.
February 2009 69