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USB and IEEE-1394 (i.Link or FireWire)The two most popular high-speed serial-bus architecture families for desktop and portable PCs are Universal Serial Bus (USB) and IEEE-1394, which is also called i.Link or FireWire. Each interface type is available in two versions: USB 1.1 and USB 2.0; IEEE-1394a and IEEE-1394b (also called FireWire 800). The USB and IEEE-1394 port families are high-speed communications ports that far outstrip the capabilities of older standard serial and parallel ports. They can also be used as an alternative to SCSI for high-speed external peripheral connections. In addition to performance, these newer ports offer I/O device consolidation, which means that all types of external peripherals can connect to these ports. Why Serial?The recent trend in high-performance peripheral bus design is to use a serial architecture, in which 1 bit at a time is sent down a wire. Because parallel architecture (used by SCSI, ATA, and LPT ports) uses 8, 16, or more wires to send bits simultaneously, the parallel bus is actually much faster at the same clock speed. However, increasing the clock speed of a serial connection is much easier than increasing that of a parallel connection. Parallel connections in general suffer from several problems, the biggest being signal skew and jitter. Skew and jitter are the reasons high-speed parallel buses such as SCSI (small computer systems interface) are limited to short distances of 3 meters or less. The problem is that, although the 8 or 16 bits of data are fired from the transmitter at the same time, by the time they reach the receiver, propagation delays have conspired to allow some bits to arrive before the others. The longer the cable, the longer the time between the arrival of the first and last bits at the other end! This signal skew, as it is called, prevents you from running a high-speed transfer rate or a longer cable—or both. Jitter is the tendency for the signal to reach its target voltage and float above and below for a short period of time. With a serial bus, the data is sent 1 bit at a time. Because there is no worry about when each bit will arrive, the clocking rate can be increased dramatically. For example, the top transfer rate possible with EPP/ECP parallel ports is 2MBps, whereas IEEE-1394a ports (which use high-speed serial technology) support transfer rates as high as 400Mbps (about 50MBps)—25 times faster than parallel ports. USB 2.0 supports transfer rates of 480Mbps (about 60MBps), which is about 30 times faster than parallel ports, and the new IEEE-1394b (FireWire 800) ports reach transfer rates as high as 800Mbps (or about 100MBps), which is about 50 times faster than parallel ports! At high clock rates, parallel signals tend to interfere with each other. Serial again has an advantage because, with only one or two signal wires, crosstalk and interference between the wires in the cable are negligible. In general, parallel cabling is more expensive than serial cabling. Besides the many additional wires needed to carry the multiple bits in parallel, the cable also must be specially constructed to prevent crosstalk and interference between adjacent data lines. This is one reason external SCSI cables are so expensive. Serial cabling, by comparison, is very inexpensive. For one thing, it has significantly fewer wires. Furthermore, the shielding requirements are far simpler, even at very high speeds. Because of this, transmitting serial data reliably over longer distances is also easier, which is why parallel interfaces have shorter recommended cable lengths than do serial interfaces. For these reasons—in addition to the need for new Plug and Play external peripheral interfaces and the elimination of the physical port crowding on portable computers—these high-performance serial buses were developed. USB is a standard feature on virtually all PCs today; is used for most general-purpose, high-speed external interfacing; and is the most compatible, widely available, and fastest general-purpose external interface. In addition, IEEE-1394 (more commonly known as FireWire), although mainly used in certain niche markets—such as connecting DV (digital video) camcorders—is also spreading into other high-bandwidth uses, such as high-resolution scanners, external hard drives, and networking. Universal Serial BusUniversal Serial Bus (USB) is an external peripheral bus standard designed to bring Plug and Play capability for attaching peripherals externally to the PC. USB eliminates the need for special-purpose ports, reduces the need to use special-purpose I/O cards, (thus reducing the need to reconfigure the system with each new device added), and saves important system resources such as interrupts (IRQs); regardless of the number of devices attached to a system's USB ports, only one IRQ is required. PCs equipped with USB enable peripherals to be automatically recognized and configured as soon as they are physically attached, without the need to reboot or run setup. USB allows up to 127 devices to run simultaneously on a single bus, with peripherals such as monitors and keyboards acting as additional plug-in sites, or hubs. USB cables, connectors, hubs, and peripherals can be identified by icons, as shown in Figure 17.1. Note the "plus" symbol added to the upper icon, which indicates that port supports USB 2.0 (Hi-Speed USB) in addition to the standard 1.x support. Figure 17.1. These icons identify USB cables, connectors, hubs, and peripherals.
Intel has been the primary proponent of USB, and all its PC chipsets starting with the PIIX3 South Bridge chipset component (introduced in February 1996) have included USB support as standard. Other chipset vendors have followed suit, making USB as standard a feature of today's desktop and notebook PCs as the serial and parallel ports once were. Six other companies initially worked with Intel in co-developing the USB, including Compaq, Digital, IBM, Microsoft, NEC, and Northern Telecom. Together, these companies have established the USB Implementers Forum (USB-IF) to develop, support, and promote USB architecture.
See "Chipsets," p. 229. The USB-IF formally released USB 1.0 in January 1996, USB 1.1 in September 1998, and USB 2.0 in April 2000. The 1.1 revision was mostly a clarification of some issues related to hubs and other areas of the specification. Most devices and hubs should be 1.1 compliant, even if they were manufactured before the release of the 1.1 specification. The biggest change was USB 2.0, which is 40 times faster than the original USB and yet fully backward compatible. USB ports can be retrofitted to older computers that lack built-in USB connectors through the use of either an add-on PCI card (for desktop computers) or a PC Card on Cardbus-compatible notebook computers. You can also use USB add-on cards to update an older system that has only USB 1.1 on the motherboard. As of mid-2002, virtually all motherboards include four or more USB 2.0 ports as standard. Notebook computers were slower to catch on—it wasn't until early 2003 that most notebook or laptop computers included USB 2.0 ports as standard. USB Technical DetailsUSB 1.1 runs at 12Mbps (1.5MBps) over a simple four-wire connection. The bus supports up to 127 devices connected to a single root hub and uses a tiered-star topology, built on expansion hubs that can reside in the PC, any USB peripheral, or even standalone hub boxes. Note that although the standard allows up to 127 devices to be attached, they all must share the 1.5MBps bandwidth, meaning that for every active device you add, the bus will slow down some. In practical reality, few people will have more than 8 devices attached at any one time. For low-speed peripherals, such as pointing devices and keyboards, the USB also has a slower 1.5Mbps subchannel. The subchannel connection is used for slower interface devices, such as keyboards and mice. USB employs what is called Non Return to Zero Invert (NRZI) data encoding. NRZI is a method of encoding serial data in which 1s and 0s are represented by opposite and alternating high and low voltages where there is no return to a zero (or reference) voltage between the encoded bits. In NRZI encoding, a 1 is represented by no change in signal level, and a 0 is represented by a change in level. A string of 0s causes the NRZI data to toggle each bit time; a string of 1s causes long periods with no transitions in the data. This is an efficient transfer encoding scheme because it eliminates the need for additional clock pulses that would otherwise waste time and bandwidth. USB devices are considered either hubs or functions, or both. Functions are the individual devices that attach to the USB, such as a keyboard, mouse, camera, printer, telephone, and so on. Hubs provide additional attachment points to the USB, enabling the attachment of more hubs or functions. The initial ports in the PC system unit are called the root hub, and they are the starting point for the USB. Most motherboards have two, three, or four USB ports, any of which can be connected to functions or additional hubs. Some systems place one or two of the USB ports in the front of the computer, which is very convenient for devices you use only occasionally, such as digital cameras or flash memory card readers. External hubs (also called generic hubs) are essentially wiring concentrators, and through a star-type topology they allow the attachment of multiple devices. Each attachment point is referred to as a port. Most hubs have either four or eight ports, but more are possible. For more expandability, you can connect additional hubs to the ports on an existing hub. The hub controls both the connection and distribution of power to each of the connected functions. A typical hub is shown in Figure 17.2. Figure 17.2. A typical USB hub with four ports.
Besides providing additional sockets for connecting USB peripherals, a hub provides power to any attached peripherals. A hub recognizes the dynamic attachment of a peripheral and provides at least 0.5W of power per peripheral during initialization. Under control of the host PC driver software, the hub can provide more device power, up to a maximum of 2.5W, for peripheral operation. A newly attached hub is assigned a unique address, and hubs can be cascaded up to five levels deep (see Figure 17.3). A hub operates as a bidirectional repeater and repeats USB signals as required both upstream (toward the PC) and downstream (toward the device). A hub also monitors these signals and handles transactions addressed to itself. All other transactions are repeated to attached devices. A USB 1.1 hub supports both 12Mbps (full-speed) and 1.5Mbps (low-speed) peripherals. Figure 17.3. A typical PC with USB devices can use multiple USB hubs to support a variety of peripherals, connected to whichever hub is most convenient.
Maximum cable length between two full-speed (12Mbps) devices or a device and a hub is 5 meters using twisted-pair shielded cable with 20-gauge wire. Maximum cable length for low-speed (1.5Mbps) devices using non-twisted-pair wire is 3 meters. These distance limits are shorter if smaller-gauge wire is used (see Table 17.1).
Although USB 1.1 is not as fast at data transfer as FireWire or SCSI, it is still more than adequate for the types of peripherals for which it is designed. USB 2.0 operates a surprising 40 times faster than USB 1.1 and allows transfer speeds of 480Mbps or 60MBps. Because it is fully backward-compatible and supports older 1.1 devices, I recommend purchasing only motherboards and add-in USB cards that conform to the faster USB 2.0 (Hi-Speed USB) standard. One of the additional benefits of USB 2.0 is the capability to handle concurrent transfers, which enables your USB 1.1 devices to transfer data at the same time without tying up the USB bus. USB 2.0 drivers were not provided with the initial launch of Windows XP but are available through system update downloads or service packs. Use the Windows Update feature to connect to the Microsoft site and download any updates as necessary. Add-on USB 2.0 cards might include their own drivers, which should be installed. USB ConnectorsFour main styles of connectors are specified for USB, called Series A, Series B, Mini-A, and Mini-B connectors. The A connectors are used for upstream connections between a device and the host or a hub. The USB ports on motherboards and hubs are usually Series A connectors. Series B connectors are designed for the downstream connection to a device that has detachable cables. In all cases, the mini connectors are simply smaller versions of the larger ones, in a physically smaller form factor for smaller devices. The physical USB plugs are small (especially the mini plugs) and, unlike a typical serial or parallel cable, the plug is not attached by screws or thumbscrews. There are no pins to bend or break, making USB devices very user friendly to install and remove. The USB plug shown in Figure 17.4 snaps into place on the USB connector. Figure 17.4. USB Series A and Series B plugs and receptacles.
Note that a Mini-A/B socket is a dual-purpose socket that can accept either Mini-A or Mini-B plugs. The newer mini plugs and sockets have plastic portions inside the connectors that are required to be color-coded as shown in Table 17.2.
Tables 17.3 and 17.4 show the pinouts for the USB connectors and cables. Most systems with USB connectors feature one or two pairs of Series A plugs on the rear of the system. Some also feature one or two pairs on the front of the system for ease of use with items that are not permanently connected.
USB conforms to Intel's Plug and Play (PnP) specification, including hot plugging, which means that devices can be plugged in dynamically without powering down or rebooting the system. Simply plug in the device, and the USB controller in the PC detects the device and automatically determines and allocates the required resources and drivers. Microsoft has developed USB drivers and included them automatically in Windows 98 and later. Windows 95B and 95C have very limited support for USB 1.1; the necessary drivers are not present in the original Windows 95 or 95A. With Windows 95B, the USB drivers are not automatically included; they are provided separately, although a late release of Windows 95—Windows 95C—includes USB support. Many USB devices will not work with any Windows 95 release, including those that have the USB support files included. Windows 98 and later have USB 1.1 support built in; however, additional drivers are required for USB 2.0 or later. In most cases, these drivers can be downloaded from Microsoft using the Windows Update feature. USB support is also required in the BIOS for devices such as keyboards and mice. This is included in all newer systems with USB ports built in. Aftermarket PCI and PC Card boards also are available for adding USB to systems that don't include it as standard on the motherboard. USB peripherals include printers, CD-ROMs, modems, scanners, telephones, joysticks, keyboards, and pointing devices such as mice and trackballs. A free utility called USBready is available from http://www.usb.org; it examines your PC's hardware and software and informs you of your PC's USB capabilities. Most PCs built in 1995 or earlier don't support USB. During 1996 most PC motherboards began supporting USB, and if your system dates from 1997 to 1998 or later, USB support is almost a certainty. One interesting feature of USB is that, with certain limitations, attached devices can be powered by the USB bus. The PnP aspects of USB enable the system to query the attached peripherals as to their power requirements and issue a warning if available power levels are being exceeded. This is important for USB when it is used in portable systems because the battery power that is allocated to run the external peripherals might be limited. You can determine the amount of power available to each port in a USB root or generic hub and the amount of power required by a USB peripheral with the Windows Device Manager (see Figure 17.5). Figure 17.5. The Power tab of the properties sheet for a USB generic hub lists available power and power usage by device.
Devices that use more than 100mA, such as the Webcam shown in Figure 17.5, must be connected to a root hub or a self-powered generic hub. Devices that use 100mA or less can be connected to bus-powered hubs, such as those built in to some keyboards and monitors.
To avoid running out of power when connecting USB devices, use a self-powered hub. Another of the benefits of the USB specification is the self-identifying peripheral, a feature that greatly eases installation because you don't have to set unique IDs or identifiers for each peripheral—the USB handles that automatically. Also, USB devices can be "hot" plugged or unplugged, meaning that you do not have to turn off your computer or reboot every time you want to connect or disconnect a peripheral. However, to prevent data loss with USB drives and storage devices, you need to use the Eject Hardware or Safely Remove Hardware feature in the Windows system tray. Click the device, select Stop, click OK, and wait for the system to indicate that the device has been stopped before you remove it. Enabling USB SupportMany systems shipped before Windows 98 was introduced in mid-1998 have onboard USB ports that were disabled at the factory. In some cases, especially with Baby-AT motherboards, there is no way to tell from the outside which systems have USB support built in. This is because many of these same systems were not shipped with the USB header cables necessary to bring the USB root hub connectors from the motherboard to the rear of the system. If USB support is disabled in the system BIOS, restart your system and locate the BIOS setup screen that refers to the USB ports. Enable the USB feature. If you see a separate entry for USB IRQ, enable this as well. After you restart the computer with a USB-aware operating system, your "new" USB root hub will be detected and the drivers will be installed if you are using Windows 98 or newer; you might need to manually install drivers with late releases of Windows 95. If your system has USB connectors present, you also will be able to use the "new" USB ports as soon as the system is rebooted after the USB drivers are installed. However, if your motherboard vendor didn't provide USB connectors, you must buy USB header cables. Before you order them, check the configuration of your motherboard's USB header pins. The standard is two rows of five pins each. Companies such as Belkin, CyberGuys, and Cables To Go sell header cables that are compatible with standard USB header pins if your motherboard supplier doesn't have the header cable in stock. Figure 17.6 shows a typical USB header cable set. Figure 17.6. A typical USB header cable set; plug it into your motherboard to connect devices to the additional onboard USB ports (if present).
One of the biggest advantages of an interface such as USB is that it requires only a single interrupt (IRQ) from the PC. Therefore, you can connect up to 127 devices and they will not use separate interrupts, as they might if each were connected over a separate interface. This is a major benefit of the USB interface. The USB interface can also be adapted to older peripherals. See the section "USB Adapters," later in this chapter, for details. USB 2.0/Hi-Speed USBUSB 2.0 (also called Hi-Speed USB) is a backward-compatible extension of the USB 1.1 specification that uses the same cables, connectors, and software interfaces, but it runs 40 times faster than the original 1.0 and 1.1 versions. The higher speed enables higher-performance peripherals, such as higher-resolution Web/videoconferencing cameras, scanners, and faster printers, to be connected externally with the same easy plug-and-play installation of current USB peripherals. From the end-user point of view, USB 2.0 works exactly the same as 1.1—only faster and with more interesting, higher-performance devices available. All existing USB 1.1 devices work in a USB 2.0 bus because USB 2.0 supports all the slower-speed connections. USB data rates are shown in Table 17.5.
If your motherboard or system features USB 2.0–compatible (Hi-Speed USB) ports, you might need to enable USB 2.0/Hi-Speed USB support in the system BIOS and install an appropriate driver. Otherwise, USB 2.0/Hi-Speed USB ports will be used as USB 1.1 ports.
See "USB Configuration Submenu," p. 406, for details. The support of higher-speed USB 2.0 peripherals requires using a USB 2.0 hub. You can still use older USB 1.1 hubs on a 2.0 bus, but any peripherals or additional hubs connected downstream from a 1.1 hub will operate at the slower 1.5MBps USB 1.1 maximum speed. Devices connected to USB 2.0 hubs will operate at the maximum speed of the device, up to the full USB 2.0 speed of 60MBps. The higher transmission speeds through a 2.0 hub are negotiated on a device-by-device basis, and if the higher speed is not supported by a peripheral, the link operates at a lower USB 1.1 speed. As such, a USB 2.0 hub accepts high-speed transactions at the faster USB 2.0 frame rate and must deliver them to high-speed USB 2.0 peripherals as well as USB 1.1 peripherals. This data rate matching responsibility requires increased complexity and buffering of the incoming high-speed data. When communicating with an attached USB 2.0 peripheral, the 2.0 hub simply repeats the high-speed signals; however, when communicating with USB 1.1 peripherals, a USB 2.0 hub buffers and manages the transition from the high speed of the USB 2.0 host controller (in the PC) to the lower speed of a USB 1.1 device. This feature of USB 2.0 hubs means that USB 1.1 devices can operate along with USB 2.0 devices and not consume any additional bandwidth. Some manufacturers of add-on USB 2.0 cards are equipping the cards with both external and internal USB 2.0 ports. How can you tell which devices are designed to support USB 1.1 and which support the emerging USB 2.0 standard? The USB Implementer's Forum (USB-IF), which owns and controls the USB standard, introduced new logos in late 2000 for products that have passed its certification tests. The logos are shown in Figure 17.7. Figure 17.7. The USB-IF USB 1.1–compliant logo (left) compared to the USB-IF USB 2.0–compliant logo (right).
As you can see from Figure 17.7, USB 1.1 is also known simply as USB, and USB 2.0 is also known as Hi-Speed USB. Also note the icons shown earlier, where the addition of the plus symbol to the standard USB trident is used to identify ports that support USB 2.0. USB On-The-GoIn December 2001, the USB-IF released a supplement to the USB 2.0 standard called USB On-The-Go. It was designed to address the one major shortcoming of USB: the fact that a PC was required to transfer data between two devices. In other words, you couldn't connect two cameras together and transfer pictures between them without a PC orchestrating the transfer. With USB On-The-Go, however, devices that conform to the specification still work normally when they are connected to a PC, but they also have additional capabilities when connected to other devices supporting the standard. Although this capability can also work with PC peripherals, it was mainly added to address issues using USB devices in the consumer electronics area, where a PC might not be available. Using this standard, devices such as digital video recorders can connect to other recorders to transfer recorded movies or shows, items such as personal organizers can transfer data to other organizers, and so on. The addition of the On-The-Go supplement to USB 2.0 greatly enhances the use and capabilities of USB both in the PC and consumer electronics markets. The first products using USB On-The-Go technologies are expected sometime in 2003; ATI's Imageon display coprocessor for PDAs and smart phones and Qualcomm's next-generation wireless chipsets are among early adopters of this technology. USB AdaptersIf you still have a variety of older peripherals and yet you want to take advantage of the USB connector on your motherboard, several signal converters or adapters are available. Companies such as Belkin and others currently have adapters in the following types:
These adapters usually look just like a cable, with a USB connector at one end (which you plug into your USB port) and various other interface connectors at the other end. In some cases, you attach standard USB and device cables to a standalone adapter, such as with the USB-to-Ethernet adapter shown in Figure 17.8. Figure 17.8. A typical USB-to-Ethernet adapter from D-Link.
There is more to these devices than just a cable: If the unit is a one-piece device, active electronics are hidden in a module along the cable or are sometimes packed into one of the cable ends. The electronics are powered by the USB bus and convert the signals to the appropriate other interface. If you cannot install a native adapter card for your device, converting it to use the USB port through an adapter is much better than not using the device at all. For example, a USB-to-Ethernet adapter such as the one shown in Figure 17.8 can enable a computer without expansion slots to connect to a broadband Internet device such as a cable or DSL modem. However, some drawbacks do exist to these adapters. One is cost: They typically cost $30–$60 or more. It can be tough to spend $40 on a USB-to-parallel adapter to drive a printer that barely cost twice that amount. In addition, other limitations might apply. For example, USB-to-parallel converters work only with printers and not other parallel-connected devices, such as scanners, cameras, external drives, and so on. Before purchasing one of these adapters, ensure that it will work with the device or devices you have in mind. If you need to use more than one non-USB device with your system, consider special USB hubs that also contain various combinations of other port types; these are sometimes referred to as multifunction USB hubs, USB port replicators, or USB docking stations. These special hubs are more expensive than USB-only hubs but are less expensive than the combined cost of a comparable USB hub and two or more USB adapters. Another type of adapter available is a direct-connect cable, which enables you to connect two USB-equipped PCs directly together using USB as a network. These are popular for people playing two-player games, with each player on his own system. Another use is for transferring files because this connection usually works as well or better than the direct parallel connection that otherwise might be used. Also available are USB switchboxes that enable one peripheral to be shared among two or more USB buses. Note that both the direct connect cables and USB switchboxes are technically not allowed as a part of the USB specification, although they do exist. Legacy-Free PCsUSB adapters might find more use in the future as more and more legacy-free PCs are shipped. A legacy-free PC is one that lacks any components that were connected to or a part of the traditional ISA bus. This especially includes the otherwise standard Super I/O chip, which integrated serial, parallel, keyboard, mouse, floppy, and other connections. A legacy-free motherboard therefore does not have the standard serial, parallel, and keyboard/mouse connectors on the back and lacks an integrated floppy controller. The devices previously connected to those ports must instead be connected via USB, ATA/IDE, PCI, and other interfaces. Legacy-free systems are primarily found on the low-end, consumer-oriented systems. For those systems, USB will likely be one of the only external connections provided. To compensate for the loss of the other external interfaces, most legacy-free motherboards feature four or more integrated USB connectors on one or two buses. IEEE-1394The Institute of Electrical and Electronic Engineers Standards Board introduced IEEE-1394 (or just 1394 for short) in late 1995. The number comes from the fact that this happened to be the 1,394th standard they published. It is the result of the large data-moving demands of today's audio and video multimedia devices. The key advantage of 1394 is that it's extremely fast; the popular 1394a standard supports data transfer rates up to an incredible 400Mbps. 1394 StandardsThe most common version of the 1394 standard is actually referred to as 1394a, or sometimes as 1394a-2000 for the year it was adopted. The 1394a standard was introduced to solve interoperability and compatibility issues in the original 1394 standard; it uses the same connectors and supports the same speeds as the original 1394 standard. The first products to use the 1394b standard were introduced in early 2003. Initially, 1394b supports 800Mbps transfer rates, but future versions of the standard might reach speeds of up to 3,200Mbps. 1394b will be capable of reaching much higher speeds than the current 1394/1394a standard because it will also support network technologies such as glass and plastic fiber-optic cable and Category 5 UTP cable, increased distances when Category 5 cabling is used between devices, and improvements in signaling. 1394b will also be fully backward-compatible with 1394a devices. 1394 is also known by two other common names: i.Link and FireWire. i.Link is an IEEE-1394 designation initiated by Sony in an effort to put a more user-friendly name on IEEE-1394 technology. Most companies that produce 1394 products for PCs have endorsed this new name initiative. Originally, the term FireWire was an Apple-specific trademark that Apple licensed to vendors on a fee basis. However, in May 2002, Apple and the 1394 Trade Association announced an agreement to allow the trade association to provide no-fee licenses for the FireWire trademark on 1394-compliant products that pass the trade association's tests. Apple continues to use FireWire as its marketing term for IEEE-1394 devices. FireWire 400 refers to Apple's IEEE-1394a-compliant products, whereas FireWire 800 refers to Apple's IEEE-1394b-compliant products. 1394a Technical DetailsThe IEEE-1394a standard currently exists with three signaling rates—100Mbps, 200Mbps, and 400Mbps (12.5MBps, 25MBps, and 50MBps). Most PC adapter cards support the 400Mbps (50MBps) rate, although device speeds can vary. A maximum of 63 devices can be connected to a single IEEE-1394 adapter card by way of daisy-chaining or branching. 1394 devices, unlike USB devices, can be used in a daisy-chain without using a hub, although hubs are recommended for devices that will be hot-swapped. Cables for IEEE-1394/1394a devices use Nintendo GameBoy–derived connectors and consist of six conductors: Four wires transmit data, and two wires conduct power. Connection with the motherboard is made either by a dedicated IEEE-1394 interface or by a PCI adapter card. Figure 17.9 shows the 1394/1394a cable, socket, and connector. Figure 17.9. IEEE-1394 port, 6-pin cable, and 4-pin cable.
The 1394 bus was derived from the FireWire bus originally developed by Apple and Texas Instruments, and it is also a part of a new Serial SCSI standard. 1394a uses a simple six-wire cable with two differential pairs of clock and data lines, plus two power lines; the four-wire cable end shown in Figure 17.9 is used with self-powered devices, such as DV camcorders. Just as with USB, 1394 is fully PnP, including the capability for hot-plugging (insertion and removal of components without powering down). Unlike the much more complicated parallel SCSI bus, 1394 does not require complicated termination, and devices connected to the bus can draw up to 1.5 amps of electrical power. 1394 offers equal or greater performance compared to ultra-wide SCSI, with a much less expensive and less complicated connection. 1394 is built on a daisy-chained and branched topology, and it allows up to 63 nodes, with a chain of up to 16 devices on each node. If this is not enough, the standard also calls for up to 1,023 bridged buses, which can interconnect more than 64,000 nodes! Additionally, as with SCSI, 1394 can support devices with various data rates on the same bus. Most 1394 adapters have three nodes, each of which can support 16 devices in a daisy-chain arrangement. Some 1394 adapters also support internal 1394 devices. The types of devices that can be connected to the PC via 1394 mainly include video cameras; editing equipment; and all forms of disk drives, including hard disk, optical, floppy, CD-ROM, and DVD-ROM drives. Also, digital cameras, tape drives, high-resolution scanners, and many other high-speed peripherals that feature 1394 have interfaces built in. The 1394 bus appears in some desktop and portable computers as a replacement or supplement for other external high-speed buses, such as USB or SCSI. Chipsets and PCI adapters for the 1394 bus are available from a number of manufacturers, including some models that support both 1394 and other port types in a single slot. Microsoft has developed drivers to support 1394 in Windows 9x and later, including Windows XP. The most popular devices that conform to the IEEE-1394 standard are camcorders and VCRs with digital video capability. Sony was among the first to release such devices (under the i.Link name). In typical Sony fashion, however, its products have a unique four-wire connector that requires an adapter cord to be used with IEEE-1394 PC cards, and Sony doesn't even call it IEEE-1394 or FireWire—it created its own designation (i.Link) instead. DV products using 1394 also are available from Panasonic, Sharp, Matsushita, and others. Non-computer IEEE-1394 applications include DV conferencing devices, satellite audio and video data streams, audio synthesizers, DVD, and other high-speed disc drives. Because of the current DV emphasis for IEEE-1394 peripherals, many FireWire cards currently offered are bundled with DV capturing and editing software. With a DV camera or recording equipment, these items provide substantial video editing and dubbing capabilities on your PC. Of course, you need IEEE-1394 I/O connectivity, which is a growing, but still somewhat rare, feature on current motherboards. IEEE-1394b Technical DetailsIEEE-1394b is the second generation of the 1394 standard, with the first products (high-performance external hard drives) introduced in January 2003. IEEE-1394b uses one of two new nine-pin cables and connectors to support speeds of 800Mbps–3200Mbps with copper or fiber-optic cabling. In addition to supporting faster transfer rates, 1394b has other new features, including
The initial implementations of IEEE-1394b use a new nine-wire interface with two pairs of signaling wires. However, to enable a 1394b port to connect to 1394a-compatible devices, there are two different versions of the 1394b port:
Beta connectors support only 1394b devices, whereas bilingual connectors can support both 1394b and 1394a devices. As Figure 17.10 shows, the connectors and cables have the same pinout but are keyed differently. Figure 17.10. Bilingual and beta 1394b connectors and cables. Many 1394b implementations use both types of connectors.
Note that bilingual sockets and cables have a narrower notch than beta sockets and cables. This prevents cables designed for 1394a devices from being connected to the beta socket. Figure 17.11 compares a beta-to-beta 1394b cable to bilingual-to-1394a cables. Figure 17.11. A beta-to-beta cable (top) compared to bilingual–to–4-pin (middle) and bilingual–to–6-pin 1394a devices (bottom).
Comparing IEEE-1394 and USBBecause of the similarity in both the form and function of USB and 1394 ports, there has been some confusion about the differences between them. Table 17.6 summarizes the differences between these technologies.
Because the overall performance and physical specifications are similar, the main difference between USB and 1394 is popularity. The bottom line is that USB is by far the most popular external interface for PCs, eclipsing all others by comparison. This is primarily because Intel developed most of USB and has placed built-in USB support in all its motherboard chipsets and motherboards since 1996. Virtually no motherboard chipsets integrate 1394a or 1394b; in most cases, it has to be added as an extra-cost chip to the motherboard. The cost of the additional 1394 circuitry (and a $0.25 royalty paid to Apple Computer per system) and the fact that all motherboards already have USB, have limited the popularity of 1394 (FireWire) in the PC marketplace. Even with the overwhelming popularity of USB, a market for 1394 still exists. Perhaps the main reason 1394 will survive in conjunction with the USB 2.0 interface is that USB is normally PC-centric, whereas 1394 is not. In other words, USB and Hi-Speed USB require a PC as the host, whereas 1394 can connect two devices directly without a PC between them. As such, 1394 can be used to directly connect a DV camcorder to a DV-VCR for dubbing tapes or editing. Even this has changed, however, as a supplement called USB On-The-Go was added to the USB 2.0 specification in December 2001. USB On-The-Go enables the same device-to-device connections as was capable in 1394 (FireWire) and essentially nullifies the one advantage 1394 had over USB. Because of the popularity and capabilities of USB, I recommend seeking out only USB peripherals over their 1394 (FireWire) counterparts where possible. Many people like to bring any comparison of USB and 1394 down to speed, but that is a constantly changing parameter. 1394a offers a data transfer rate more than 33 times faster than that of USB 1.1, but is only about 83% as fast as USB 2.0. However, 1394b is about 66% faster than USB 2.0. Because both USB 2.0 and 1394a (FireWire) offer relatively close to the same overall capabilities and performance, you make your choice based on which devices you intend to connect. If the digital video camera you want to connect has only a 1394 (FireWire/i.Link) connection, you will need to add a 1394 FireWire card to your system, if such a connection isn't already present on your motherboard. Most general-purpose PC storage, I/O, and other devices are USB, whereas only video devices usually have 1394 connections. However, many devices now offer both USB 1.1/2.0 and 1394a interfaces to enable use with the widest range of computers.
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