USB General

What is "USB"?

USB stands for Universal Serial Bus, which is an interface standard developed by an industry group known as the USB Implementers Forum (USB-IF).
The USB standard enables peripheral units to be connected using standardized common connectors.
Moreover, by adding a connecting node known as a hub, USBs can provide a range of user-friendly features such as connection of up to 127 units and support for "hot plug-in", whereby units can be recognized via Plug & Play.
Most computers today incorporate a USB interface. The faster USB 2.0 standard was developed in order to support peripheral units such as printers and scanners.
With a USB 2.0 interface, both the host and peripheral unit to be connected must support the USB 2.0 standard for the interface to work.

(2006/08)

Where are USB related products positioned in a system?

Basically, the host controller incorporated in the host system interfaces with the function controller in the peripheral unit.
When you want to attach more than one peripheral unit to a single host, USB ports must be added to the system. Ports can be added by using a USB hub. The hub controller incorporated in the hub relays the USB connection between the host and the peripheral units.
Note that peripheral units that incorporate an IDE interface, such as DVD and CD-ROM drives, are connected via an IDE bridge.

(2006/08)

How can I obtain a driver for the USB host controller and hub controller?

In a Windows or Linux environment, these drivers are basically supported by the OS.
For an embedded real-time OS such as uITRON or VxWorks, the drivers will be supplied by the software vendor.
Please see the list of vendors at the bottom of each product page on our USB website.

(2006/08)

What are the USB specifications?

For the USB specifications, see the USB specifications, which can be downloaded from the following USB Specification:
http://www.usb.org/developers/docs/usb_20.zip

What is the difference between USB 1.1 and USB 2.0?

Their respective transfer rates are specified as follows.
USB 1.1: Low-Speed (1.5 Mbps:LS),Full-Speed (12 Mbps:FS)
USB 2.0: Low-Speed (1.5 Mbps:LS),Full-Speed (12 Mbps:FS),Hi-Speed (480 Mbps :HS)

Generally, USB 1.1 is described as referring to LS/FS and USB 2.0 as referring to HS, but this is not accurate. Currently, all USB devices that are developed must comply with USB 2.0.
Any of LS, FS, or HS can be used to indicate the transfer rate.

Can I use my USB IC device immediately after purchase?

All NEC Electronics USB LSI products have passed the USB-IF certification test, but it is still necessary for customers to ensure that each unit in which an NEC Electronics USB LSI product is used has passed the USB-IF certification test and been licensed when that unit is developed or sold.
Please check with the USB Implementers Forum (USB-IF) for more details.

(2006/08)

My PC peripheral unit with a USB interface doesn't work. Can I apply to the manufacturer of the USB IC device for technical support?

The operation of a PC peripheral unit with a USB interface is not only determined by the USB LSI; it also heavily depends on other factors such as the board on which the LSI is mounted or the components that incorporate the LSI, as well as other circuitry and the design and characteristics of the software. These factors are out of the hands of the IC manufacturer, so only the manufacturer of the peripheral unit itself can provide technical support.
If your peripheral unit is an NEC personal computer peripheral and you live in Japan, please contact the NEC 121 Contact Center.

(2006/08)

What is the approximate transfer rate supported by USB 2.0?

For data itself, the transfer rate is 480 Mbps (60 Mbytes/s).
Like other communication standards, the format of the packets that are transmitted with USB is specified, and information such as addresses or CRC is appended for transfer.

Moreover, there is an idle period between packets, and the transfer speed is not a uniform 60 Mbytes/s over the whole duration of the transfer.
The transfer rate depends also on the system, and can vary largely depending on limitations on the PCI side, limitations of USB devices, PC performance, the driver, and so on.

In a PC environment, NEC Electronics evaluations have found the transfer rate using USB 2.0 storage devices (HDD) to range between approximately 20 Mbytes/s and 25 Mbytes/s.