Universal Serial Bus (USB)

Raycomm are a UK based, leading developer of custom software and electronic design solutions for innovative technological products and systems.

USB is a serial bus standard to interface devices. It was designed to allow peripherals to be connected using a single standardised interface socket to improve plug and play capabilities because it allows devices to be disconnected without rebooting the computer (hot swapping).

Other useful features include powering low powered devices without the need for an external power supply. USB be can be used to connect a host of “standard” devices such as mice, keyboards, PDAs, gamepads, joysticks, digital cameras and printers. Whilst USB was conceived for personal computers it has become much more commonplace on a range of consumer and industrial devices.

Each device connected to a USB host defines an associated set of pipes (logical channels) these pipes are directional connections from Host to device or vice versa. They terminate on the device at an endpoint. These endpoints can transfer data in one direction only. (Each USB device can have 32 active pipes -16 in to host and 16

USB Commands

USB hardware consists of a host controller this is the USB hardware most often found in a personal computer. Different Device classes then can be connected to the host controller.

The device class defines expected behaviour and commands that the client must support in order for it to be a defined device class. There is also a class called vendor specific which covers any custom USB based interface that may be required. If a device conforms to a published device class then often the operating system will implement a generic driver for that class of USB device. Vendor Specific devices require a custom driver to be written for the host environment.

Defined device classes

• 0x01: USB Audio Device class, USB headsets, external sound cards.
• 0x03: USB Human Interface Device class (HID), keyboards, mice
• 0x06: Power
• 0x07: Printer etc
• 0x08: USB Mass Storage Device class used for USB flash drives, memory card readers, digital audio players etc.
• 0x09: USB hubs.
• 0x0B: Smart Card readers.
• 0x0E: USB Video Device class, webcam-like devices, motion image capture devices.
• 0xE0: Wireless controllers, for example Bluetooth dongles.
• 0xFF: Vendor Specific

USB Data Rates

There are currently 3 supported data rates with a fourth likely to appear in products in the next couple of years.

• Low-speed (USB 1.0) rate of 1.5 Mbit/s (192kB/s)
• Full-speed(USB 1.1) rate of 12 Mbits/s (1.5MB/s)
• Hi-speed (USB 2.0) rate of 480 Mbit/s (60 MB/s)
• Super-Speed (USB 3.0) rate of 4.8 Gbit/s (600MB/s)

USB on the Go

USB On-The Go (USB OTG is a supplement to the USB 2.0 specification. USB OTG changes the master slave relationship such that a device can act as a Host (master) or Device (slave).

An example could be a printer that knows how to grab documents from a USB flash drive and print them but could also be used as a printer in the normal way.

Wireless USB

Wireless USB (WUSB) is a short-ramge high bandwidth wireless communication protocol. It is based on WiMedia Alliances Ultra-WideBand (UWB) common radio platform. It is capable of 480 Mbit/s at distances up to 3 metres and 100Mbit/s at up to 10 metres. It is designed to operate in the 3.1 to 10.GHz frequency range.

Wireless USB is a protocol that sits on top of a UWB platform. The same platform is also used Bluetooth and Wireless 1394 (FireWire).

The architecture allows up to 127 devices to connect directly to a host. Unlike normal USB because there are no wires Hubs are not required.

USB Design

Adding USB to a custom project usually involves the use of the Vendor specific class to allow the correct custom commands to be used. Raycomm have the expertise to not only implement the interface hardware and software, but also to develop the necessary drivers for Windows and or Linux.

Sometimes the USB interface and drivers are supplied such as with the FTDI range of USB devices. These devices allow the replacement of serial interfaces with a USB one. Raycomm has experience of developing a custom API that supports the specific protocol and commands of the device. This means the customer doesn’t need to understand the complexities of the FTDI device but just uses a high level interface.