Texas Instruments 4Q 2006 Universal Serial Bus USB, Speed, Transfer Type, USB-to-Serial Bridge

USB Hub Controllers and Peripheral Devices 25

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Universal Serial Bus (USB)

The USB standard defines a bus product that requires a host controller and enables plug- and-play connectivity. The most recently released final specification, USB 2.0, defines high speed and allows complete backward compatibility with USB 1.1.

USB products fall into three categories: hubs, host controllers and peripherals. USB 1.1 sup- ported speeds of up to 12 Mbps and cables up to 5 meters long for these devices. USB

2.0extends the connection speed to 480 Mbps to support next-generation peripherals of higher-performance PCs and applications. USB 2.0 officially defines three speeds: low (1.5 Mbps), full (12 Mbps) and high (480 Mbps). The lowest speed is ideal for human interface devices such as a mouse, game pad or keyboard; while full speed is well suited for “data dumps” to the PC via digital still cameras, PDA cradles and flash-card readers. Modems, printers, scanners and storage drives are just a few of the items that can take advantage of USB’s highest speed specification.

The USB On-The-Go (OTG) supplement to USB

2.0specifies a new class of devices aimed at the portable market. USB OTG defines devices that can operate as standard USB peripherals when connected to a standard USB host controller.

However, these same devices can operate as reduced-function host controllers to support selected USB OTG peripheral devices. End-equipment manufacturers can specify what type of peripherals their devices will support when in OTG host mode. This new specification allows easy sharing of contact information between USB OTG PDAs and cell phones or printing of photographs directly from an OTG- enabled digital still camera without a PC.

Technical Information

Speed

•The USB 2.0 standard defines three speeds: low speed (LS) 1.5 Mbps, full speed (FS) 12 Mbps and high speed (HS) 480 Mbps. It requires full backward and forward compatibility for devices and

cables. All three modes offer both asyn- chronous and isochronous (real-time) data transmission over a simple and inexpensive 4-wire cable to meet requirements of peripherals including keyboards, mice, printers, speakers, scanners, external storage devices and digital still cameras.

Transfer Type

•USB 2.0 defines four types of transfers: bulk, control, interrupt and isochronous. Bulk transfer is intended for applications such as printers, scanners and mass storage, where latency isn’t critical but accuracy is. All devices must include control transfers for configuration. Interrupt transfer is for devices such as mice, keyboards and game pads that must receive the host’s or device’s attention periodically. Isochronous transfer offers guaranteed delivery time but no error- checking or automatic retransmission of data received with errors, making it the better choice for audio or video applications.

RS232/IrDA Serial-to-USB Converter

TUSB3410

Get samples, datasheets, EVMs and app reports at: www.ti.com/sc/device/TUSB3410

USB-to-Serial Bridge

The TUSB3410 provides an easy way to move a serial-based legacy device to a fast, flexible USB interface by bridging between a USB port and an enhanced UART serial port. The TUSB3410 contains all the necessary logic to communicate with the host computer using the USB bus.

Key Features

•USB full-speed-compliant: data rate of 12 Mbps

•8052 microcontroller with 16 Kbytes of RAM that can be loaded from the host

or from external onboard memory via an I2C bus

•Integrated, enhanced UART features including:

•	Programmable software/hardware flow
	control
•	Automatic RS-485 bus transceiver
	control, with and without echo
•	Software-selectable baud rate from
	50 to 921.6 kbaud
•	Built-in, two-channel DMA
	controller for USB/UART bulk I/O
• Evaluation module to jump-start USB
development or for use as a complete
USB-to-RS-232 converter

	Out			SOUT
Host						Legacy
			TUSB3410			Serial
(PC or OTG DRD)	USB
					SIN	Peripheral
		In

TUSB3410 data flow.

Applications

•Handheld meters

•Health metrics/monitors

•Any legacy serial device that needs to be upgraded to USB

Texas Instruments 4Q 2006 Interface Selection Guide