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USB is a hardware interface with defined protocols that enable a host computer

to communicate with a variety of peripheral devices. As Chapter 1 explained,

PC software can access some USB devices as virtual COM ports (VCPs). This

chapter introduces USB and how it relates to virtual COM-port devices.

The USB 2.0 specification is the main document that defines the interface.

USB specifications are available from the USB Implementers Forum (USB-IF)

(www.usb.org). For more a more detailed discussion of USB protocols, see the

specification or my book, USB Complete: Everything You Need to Develop Cus-

tom USB Peripherals.

  

An RS-232 interface assumes nothing about the contents of the data being

transferred. The computer at each end of the cable can use any method to

define what the data means.

In contrast, USB is an intelligent interface with defined protocols. Every USB

communication is between a host and a device. The host manages communica-

tions on the bus, and devices respond to communications from the host. The