THEDESIGNCYCLE
ADVANCED TECHNIQUES FOR DESIGN ENGINEERS
■ BY FRED EADY
A REASONABLE REPLACEMENT
FOR RS-232
I'VE FINALLY BEEN PUSHED OVER THE EDGE. I'm going to include USB
interfaces on subsequent Design Cycle projects that require serial
communications with a personal computer. This has been a long time
coming as I have been purposely steering clear of anything USB in our
Design Cycle projects. My gun-shy attitude towards USB is rooted in my
past experiences with attempting to understand and apply USB technology
to my embedded designs. I recall trying to understand all of the tables
and states that the USB protocol required for proper operation, and the
tremendous coding effort that, at the time, was necessary to build a
USB interface. All of that stuff turned me off to using USB in my projects.
I've been peeking through the fence at stand-alone USB
ICs that are capable of replacing the venerable RS-232
interface ICs I've grown to love over the years. The new
generation of USB ICs claim to be able to fall into the
place of legacy RS-232 drivers with nothing more than
a printed circuit board (PCB) change. That's fine on the
hardware side. However, what really has to be done on
the firmware side to make the transition? Is the transition to
the USB firmware interface driver a "no-brainer," as well?
THE SILICON LABORATORIES CP2103
The majority of the microcontroller projects I do for
Design Cycle include an RS-232 interface in the design.
The advantages of implementing a microcontroller RS-232
interface are many. For instance, a microcontroller
equipped with an internal UART can easily transfer data
between itself and another microcontroller, or itself and
a PC application. A microcontroller RS-232 interface is
also an easy way to provide visual indicators for human
consumption. A good example of a microcontroller
application using its RS-232 interface to convey
information to a human via a PC terminal emulator
application is the WLAN Phoenix. Not only does the
Phoenix microcontroller application display IP and MAC
addresses, the embedded RS-232 interface allows the
personal PC emulator application to pass human-generated information from the PC to the microcontroller.
According to the CP2103
datasheet, using it to
replace the RS-232
■ PHOTO 1. Most of the
Evaluation Kit printed
circuit board is dedicated
to allowing the user access
to the CP2103's hardware
resources. The SP3243EU
RS-232 converter IC is
included to allow easy
connection to a device
equipped with a standard
RS-232 interface. The USB
side of the Evaluation Kit is
intended to connect to a
personal computer.
68
February 2009