15

 

"



% 




Vendors who offer USB controllers designed specifically for use in virtual COM
ports are Future Technology Devices International (FTDI) (www.ftdi-
chip.com), Prolific Technology, Inc. (www.prolific.com.tw), and Silicon Labora-
tories (www.silabs.com). The chips from these vendors function in similar ways.
These chips are sometimes called USB to UART bridges. This chapter describes
FTDI’s chips and driver.

FTDI has several USB interface chips that manage enumeration and other bus
communications completely in hardware. The company provides free USB vir-
tual COM-port drivers for use with the chips. The chips don’t require any
USB-specific firmware at all but can store device-specific descriptor values in
EEPROM if desired. A microcontroller or other CPU interfaces to the control-
ler via a serial or parallel interface. The CPU provides COM-port data for the
controller to send to the USB host and retrieves COM-port data received from
the USB host.