THE DESIGN CYCLE
Microchip USB Device Firmware
Framework; Low Pin Count USB
Development Kit; PICkit2; PICkit3;
C18 C Compiler; PIC18F14K50
Ellisys USB Explorer 200
USB Protocol Analyzer; Ellisys
USB Analysis Software
JUST ANOTHER WALK
IN THE USB PARK
Believe it or not, you don’t have
to write a single line of code to build
a USB-to-UART bridge with the
PIC18F14K50. All of the code we have discussed — with
the exception of my custom Product String — is contained
within a CDC example project that is bundled into the
firmware framework. So, we can build up our own unique
version of the low pin count kit and simply load the CDC
code into our PIC18F14K50 using a PICkit2 or PICkit3
and BOOM! A USB-to-UART bridge comes to life. In this
respect, the PIC18F14K50 also qualifies as a “drop-in
replacement” for legacy RS-232 interfaces.
■ SCREENSHOT 6. The strings are used in various places
for human benefit. For instance, if you look at the COM
port properties entry in Device Manager, you’ll find the
“NUTS AND VOLTS USB-TO-UART” string behind the
Location description under the General tab.
■ PHOTO 3. This is a simple straight-thru affair. Note the
location of the pin 1 key and the socket polarization tab on the
10-pin plug versus the orientation of the DE- 9 IDC connector.
No cable twisting is necessary. However, note that the ribbon
cable is stripped to
nine strands to
mate with the DE- 9
If you plan to interface to a PC COM port, you’ll need
a female DE9 connector for the null modem interface.
As you can see in Photo 3, I used a piece of ribbon
cable and a couple of common IDC connectors to
assemble my DCE interface.
Scratch another notch into the handle of your
USB gun. You’ve just added another USB device to your
Design Cycle. NV
CONTACT THE AUTHOR
■ Fred Eady can be contacted via email at firstname.lastname@example.org.
June 2009 21