Protocol analysis
R&S
®
RTP
801User Manual 1337.9952.02 ─ 12
● The USB protocol..................................................................................................801
● USB 2.0 configuration........................................................................................... 806
● USB 2.0 trigger......................................................................................................810
● USB 2.0 decode results........................................................................................ 819
● Search on decoded USB 2.0 data.........................................................................820
13.18.1 The USB protocol
The USB protocol was developed, starting in 1996, by the nonprofit organization USB
Implementers Forum, Inc. (USB-IF), formed by Compaq, Hewlett-Packard, Intel,
Lucent Technologies, Microsoft, NEC, and Philips. The purpose was to provide a com-
mon "plug-and-play" solution to replace a multitude of interfaces for the communication
between computers and devices. It should allow even unskilled users to easily connect
many devices to a PC. USB was originally used for devices that feature low signalling
rates (up to 1.5 Mbit/s), especially human interface devices like mouse, joystick or key-
board. With the release of USB 2.0 in April 2000, devices such as printers, cameras
and mass storage media were enabled to exchange data at faster rates (up to
480 Mbit/s). Also, the high-speed protocol HSIC (High Speed Inter Chip) is used for the
communication between on-board devices.
Figure 13-21: USB Topology: mass storage device, printer, USB hub, and mouse (human interface
device) connected to a USB host
More information, including the USB specification, is available online within the web
domain http://usb.org.
This chapter provides an overview of protocol characteristics, data transfer, packet
structure, address and endpoint formats of USB and trigger possibilities.
USB characteristics
Main characteristics of USB are:
●
Four-wire design: USB requires a shielded cable containing four wires. Two of
them, called D+ and D-, form a twisted pair (for low speed, they may not be twis-
ted). These data lines transmit differential data signals and single-ended signal
states, both referenced to a third wire: the GND or ground. The fourth wire, called
VBUS (voltage bus), carries a nominal 5 V supply, which may be used to power a
device.
●
Host-to-device communication: in USBs "speak-when-spoken-to" protocol, commu-
nication is always initiated by the host. Consequently, there is no direct communi-
cation between USB devices, apart from few exceptions.
USB (option R&S
RTP-K60)
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