Silicon Imaging USB 2

The high speed image capture and connectivity market is about to undergo a revolution. The need for purchasing and installing

a custom frame grabber or IEEE-1394 interface card will soon become a distant memory. The new standard will be to connect your high speed megapixel machine vision and line scan cameras with a single 4-wire cable directly into a 480Mbit/sec (megabits per second) USB 2.0 port, soon to be found in every new motherboard produced with Intel P4 chipsets. These new USB 2.0 vision cameras will transfer precision 8 or 12-bit digital gray scale or color image data, eliminating the sampling jitter of traditional analog RS-170 or NTSC systems, at speeds 40x faster than the predecessor USB1.1 and 20% faster than Firewire (aka. IEEE-1394 or Sony i-link) devices. This interface will also provide bi-directional serial communication for camera setup and control, triggering, strobing and other I/O signaling. One of the most convenient benefits, especially for those imaging executives and sales engineers traveling with the latest lightweight laptops, is not having to carry an additional power supply; these cameras will be powered thru the same USB cable. For the vision system end-user, the benefit will be a lower system cost than previous camera and frame grabber solutions and plug-n-play installation.

The Silicon Imaging MegaCamera-2.0 family offers a broad range of models based on desired resolution, frame rates, capture method and cost, each optimized for full USB 2.0 speed performance. All cameras provide 12bit precision digitizing, sampling rates to 50MHz, software programmability of exposure, gain, clock, 8/12 bit transfer and triggering modes, very small size and bus powered capability. The SI-3200 is the worlds first 3.2 Megapixel USB 2.0 camera, capable of 2048x1536 at 15fps or 1920x1080 HDTV resolution at 24fps. An 8x digital pan/tilt/zoom function enables a region of the image to be readout at video rates and moved through the scene for video conferencing and surveillance applications. For lower cost application the SI-1300 provides 1280x1024 resolution at 30fps. For scientific analysis, medical imaging and stop-motion machine vision applications the SI-1024F has 1024x1024 resolution up to 30fps with large 12um pixels, Full-Frame shutter, binning, adaptive readout and windowing. For high speed motion capture and sports analysis, the SI-320F can capture and recording 320x240 resolution video at over 500 frames per second. All models are available in either monochrome or Color RGB Bayer formats with products starting under $995. Yes, this includes a cable.

The Universal Serial Bus (USB) standard was originally developed in 1995, to minimize the number of ports in the back of the PC. The major goal of USB was to define an external expansion bus which makes adding peripherals to a PC low cost and as easy as hooking up a telephone to a wall-jack. USB featured a maximum bandwidth of 1.5Mbit for low speed devices such as mice and keyboards, and a maximum bandwidth of 12Mbit for higher speed devices such as web cams, printers, scanners and external CD-RW drives. Frustrated by Apples royalty fees on firewire devices, in April 2000, seven industry-leading companies, consisting of Compaq, Hewlett Packard, Intel, Lucent, Microsoft, NEC, and Philips published the specifications for USB2.0. It has taken approximately 2 years for USB 2.0 to become adopted as a mainstream USB1.1 replacement. In just a few short months USB 2.0 will be the high speed PC peripheral connectivity choice over IEEE-1394.

The USB 2.0 specification extends the maximum speed of the connection from 12 Mbps on USB 1.1 up to 480 Mbps (60MBytes/sec). This enables the transfer of 1920x1080 images at 24fps (frames per second) for high-definition video conferencing or 320x240 images at 500fps for high speed video motion analysis. The transition to USB 2.0 will be seamless, since USB 2.0 is both forward and backward compatible with USB 1.1. Older peripherals will simply plug into new USB 2.0 capable PCs and Hubs. The USB connectors and cables are even identical. It is even possible for a high speed USB 2.0 device to plug into a legacy USB1.1 port and simply operate at reduced throughput. Both Hi-Speed USB 2.0 and original USB 1.1 peripherals can operate on a computer at the same time. The new USB 2.0 expansion hub design manages the transition of the data rates between the high speed host and lower speed USB peripherals, while maintaining full bandwidth utilization. Up to 127 USB peripherals with 5 levels of hubs can be connected to a single USB host controller. With 5 Meters (16.4 feet) of cabling between devices, a network of cameras, sensors, data acquisition, and I/O devices can physically extend up to 30 Meters (98 feet) from the PC. A peripheral can either be self-powered or bus-powered, with up to 500mA of consumption. To satisfy the needs of low-power embedded and portable computer applications, a power-management mechanism is also incorporated.

A USB device can be plugged in anytime, even while the PC is

turned on. The installation process is truly plug-and-play; no hassles with jumpers, IRQ settings, Interrupt or incorrect drivers. To achieve this almost magical connection process, the PC and peripheral, in our example the camera, go thru a detailed electrical handshaking and data setup procedure. A high-speed camera initially attaches to the PC USB controller as a classic full-speed (12Mb/sec) device. The camera then signals it is high-speed capable. The host controller responds to indicate it is also USB 2.0 capable and begin communicating at the high-speed rate. When the PC operating system detects that a USB device has been plugged in, it automatically assigns the peripheral a unique address. All further communication to that device uses this address, thereby distinguish it from other devices on the bus. The PC then learns the devices capabilities, by requesting its "descriptors". This information is stored within the power and bandwidth needs and required driver. From this information, the PC automatically loads the device’s driver into the operating system and the device is ready for use. This sign-on process is called Enumeration.

In USB, the PC is the master and the peripherals are slaves. The PC makes requests and peripherals respond. A typical USB transaction has three stages. First, a Token packet is sent by the PC with the address of the device and an indication of the desired direction of data transfer. If data is being sent to the peripheral, such as camera setup commands, it is an OUT request. If data will be sent from the peripheral to the PC, such as image data input from a camera, it is an IN request. Next is the data packet transfer stage. A data packet can have up to 3072 bytes along with a CRC value for error checking. The third stage is the handshake. Once the data has arrived successfully, a packet is sent to ACK or acknowledge it. For streaming data which do not require error checking or handshaking, for slightly reduced overhead, can be sent in isochronous mode. For guaranteed data accuracy, in Bulk mode, packets with errors are retransmitted. Every 125usec a bus synchronization signal call Start-of-microframe is issued. During each microframe the PC will perform multiple data transfers. For maximum bandwidth utilization, up to 13 packets containing 512 bytes of data can be transferred during each microframe,. This translates to over 53 Mbytes/sec throughput (13 packets/uFrame * 512 bytes/packet * 8uFrames/ms), including protocol and handshake overhead. From the programmers perspective,

In May 2002, Intel sealed the success of USB2.0 connectivity. Intel released a family of chipsets called 845E, 845G and 845GL for both the Pentium-4 and Celeron processors. These chipsets which include the ICH4 South Bridge chip, all have an embedded USB2.0 enhanced host controller interface and hub, capable of supporting up to 6 high or low speed ports. PC OEMs will no longer need to purchase and incorporate an additional peripheral IC to implement the interface; it will effectively come for free. Further accelerating market domination, Intel also released a family of motherboards based on these new chipsets. The next day after the debut, Dell released its first desktop machine with this new chipset architecture, the 4300S, with a retail price of $789! Yes, that includes a monitor.

Since the ICH4 connects directly to the memory controller, (aka. North Bridge chip), over a 266MB/s (32bit/66MHz) hub interface, it can simultaneously move data from the USB2.0 at maximum rates without reducing the bandwidth capacity of the 32bit/33MHz PCI bus. For applications requiring multiple high speed simultaneous capture, additional USB2.0 PCI adaptor cards can be added into the system without saturating the bus. This new PC architecture provides the same system improvement for digital video capture as the AGP bus provided for increased throughputs to a display. The result is more inputs, speed, resolution, or frame rate at lower costs.

Earlier this year, there was some industry buzz that Microsoft may not be strongly backing the emerging USB2.0 standard, as the supporting drivers were not included with the launch of WIN-XP. The main issue was that the USB2.0 drivers were not completed at the time of launch of XP and there were not enough peripherals on the market yet for testing. The delay was simply to prevent potential incompatibilities, reminiscent of the early days of Firewire, and to insure clean installation and operation for the new generation of peripherals. Microsoft has since released a driver for Windows XP and has upgrades planned for Windows Me and Windows 2000. However, Microsoft has stated it will not provide USB 2.0 driver support on Windows 9x or earlier Windows operating systems. Adaptec, a recognized leader in USB2.0 Adaptor cards and hubs, has jumped in to fill this market need by developing and delivering drivers for their USB2.0 host products for WIN 98, XP, ME and 2000. The Linux community has even recognized the imminent growth of USB2.0 and has already released driver support in their latest kernel.

CameraLink, a connectivity standard for industrial digital cameras and frame grabbers, will continue to be the interface of choice for the highest speed imaging applications. In its base configuration, CameraLink can transfer at up to 1.6 Gb/sec. In Full configuration, using 2 cables, the rate is extended up to 4.8 Gb/sec. This extremely high throughput has enabled the Silicon Imaging SI-3170 CameraLink camera to achieve sustained real-time 30fps 12-bit video at 3.2 Megapixel resolution, or 1.2 Gb/sec peak transfer speeds. To meet the increased transmission capacity of this interface, CameraLink frame grabber manufacturers have recently expanded their product offerings to include 32bit/66MHz and 64bit/66MHz PCI cards with multiple channel input capability. At the entry level, 32bit/33MHz PCI cards provide price/performance value with products starting as low as $695. No, that does not include the cable.

The primary difference of IEEE-1394 is its peer-to-peer topology, which enables peripherals, such as a VCR and television, to communicate between each other without the need for a master PC. This feature does not provide any value in a system where the PC is doing your image capture, processing, display, storage and networking. The USB Master/Slave architecture was chosen as the best way to keep peripheral costs to a minimum. Silicon vendors estimate that 1394 peripheral controllers require four to five times more gates to implement the interface than a comparable USB 2.0 peripheral. The "smarts" are placed on the PC side, eliminating the costly intelligence required for every USB peripheral device. In addition, USB has remained royalty free, making inexpensive peripherals possible and avoiding the burden of licensing.

Category	USB 2.0	IEEE-1394a	CameraLink
Topology	Master-slave, OTG	Peer-to-peer	Master-slave
Bit rates	480 Mbits/s	400 Mbits/s	1.6 Gbit/s, 4.8 Gbit/s
Transaction intervals	125 microseconds	125 microseconds	Synchronous
Bus master	Dedicated	Allocated at bus reset	PC
Signaling	Current mode differential	LVDS, optical	Multiplexed LVDS
Cable Distance	5 M, Up to 30M with 5 hubs	4.5 M, more with repeaters	10M max
No. of Wires	4	6	26, 52
Bus Power Consumption	Up to 500mA @ 5V	Up to 1.5A	no
Licensing	No	Licensing agreement and royalties	No
Main applications	PC-centric	Consumer electronics	PC-centric
Devices in network	127	63	1

The base link speed of USB2.0 at 480Mbit/sec is 20% faster than Firewire's 400Mbit/sec rate. For the past two years, 1394 proponents would show you a specification for 1394b with supported data rates in excess of 800Mbit/sec. To date, no silicon manufacturer is in production with 1394b higher data rate devices, primarily due to lack of market demand. When, and if, these devices are finally introduced to the market, they will have several strikes against its implementation. First, they will likely be highly targeted for Disk Drive Interfaces not imaging. Second, the user will still be required to purchase a custom interface card which will immediately saturate the PCI bus, leaving no bandwidth for other devices to communicate. Third, the interface will not achieve the higher data rates necessary for CameraLink connectivity applications.

Due to the growing need for a direct interconnectivity between mobile devices (e.g. digital cameras, PDA, cell phones) and computer peripherals (e.g. printers, disk drives, home gateways) the USB 2.0 specification was recently supplemented with "On-The-Go" (OTG) capability. With this simple addition, an OTG peripheral will have limited host type capability and enable direct data transfer, peer-to-peer, to another USB or OTG peripheral, without PC intervention. This is just another stake in the heart for IEEE-1394. But for now, both USB 2.0 and 1394 are expected to co-exist on many consumer systems into the foreseeable future.

With millions of powerful 2.4 to 3.0GHz motherboards with USB 2.0 built-in to ship this year, with no additional cost to the user, there is no doubt that USB2.0 will soon become the de-facto standard for vision cameras and high speed image processing. According to the In-Stat/MDR report "USB: The Universal Connection," USB 2.0 enabled devices will gain rapid acceptance in the marketplace with a 220% compound annual growth rate predicted between 2001 and 2006. USB 2.0 will be the preferred connection for most PC peripherals, whereas the IEEE 1394 interface will coexist with USB2.0 in audio/visual consumer electronic devices. The USB2.0 will achieve faster speeds and lower costs than IEEE-1394. However, CameraLink will continue to be king of speed. For application requiring direct interconnectivity without a PC, you can plug in with OTG. A new generation of high performance digital cameras will help accelerate the adoption of USB2.0 in the imaging and machine vision market. The result for the system user and instrument developers will be increased resolutions, higher frame rates, lower costs, smaller size, increased portability and most likely a new generation of products to offer to offer to the market.

For more information on the Megacamera2.0, Cameralink and USB2.0 visit www.siliconimaging.com!