IEEE 1394 Port Overview

Compared to the performance you've come to expect from your PC, serial ports are slow at best. They are constrained not only by the pragmatic aspects of their design-UART chips and the clocks that control them-but also by the medium through which the signals travel. Single-ended signals and cables of dubious quality are the communications equivalent of unleashing a go-kart with a lawnmower engine on an Autobahn that's unfettered by speed limits. The chances your data will get where its going unscathed are slim and, even if successful, the trip will be slow. As long as the medium remains the same, improvements in serial signal speed will be chancy, if possible at all.

The best way to accelerate the serial trip is to redefine both the medium and the method. The IEEE embarked on exactly that goal and is working on a proposal called P1394 to be the serial port of the future. The goal of the effort is to give computer and peripheral makers a low cost but high speed interface for linking devices and systems. Rather than replacing the RS-232C port alone, proponents see P1394 as a substitute for all the odd and varied ports on the back of your PC. P1394 has the potential for replacing not only your serial port but the parallel port, SCSI port, even the video connector.

Cross the slowest port in your PC with the most cantankerous one, and what do you get? Not an engineer's nightmare but a vision of the future called P1394. Although this up and coming standard combines the serial technology of today's laggardly RS-232C port with the intelligence of SCSI protocol, it takes the best instead of worst of each and makes an interconnection system with the speed of local bus, the wiring ease of MIDI, and economy in keeping with today's plunging PC prices. Add to the list of mandatory equipment on your next PC another port.

More than the next generation of serial communications, P1394 will likely be the connection that brings mass market simplicity to multimedia. One connection could do it all, linking as many as 16 peripherals. Advocates of P1394 imagine it linking PCs not just to traditional devices like CD ROM drives, hard disks, modems, printers, and scanners but also to video cameras and stereo systems. Easier to plug together than ordinary stereo components, P1394 eliminates the wiring confusion that scares technophobes from trying and using computer technology. If you can manage plugging your PC into a wall outlet, you can connect the most elaborate multimedia system. In short, P1394 is key to pushing computing technology into home and everyday entertainment.

Development of the new standard began nearly a decade ago in September 1986 when the IEEE (Institute of Electrical and Electronic Engineers) assigned a study group the task of clearing the murk of thickening morass of serial standards. Hardly four months later (in January 1987), the group had already outlined basic concepts underlying P1394, some of which still survive in today's standard-including low cost, a simplified wiring scheme, and arbitrated signals supporting multiple devices. Getting the devil out of such details as operating speed and the technologies needed to achieve it, took years because needs, visions, and visionaries changed. Consensus on the major elements of the standard-including the connector and the bus management-came only in 1993, and the standard reached final form in late 1994. Achieving its worthy goals required four breakthrough new technologies, including a novel encoding system that made high speed safe for serial data, a self-configuration system that moved the headaches of setup from users to the port circuitry, a time based arbitration system that guarantees all of the many devices linked to a single port have fair and guaranteed access, and a means of delivering time critical data like video without affecting the transfer of serial data.

P1394 truly offers something for everyone-today's relatively skilled PC user, tomorrow's casual home user, and even machine makers.

For manufacturers, the cost of P1394 may prove most alluring. P1394 has the potential of reducing the cost of external connections to PCs both in terms of money spent and panel usage. Both of these savings originate in the design of the P1394 connector. P1394 envisions a single 6-wire plastic connector replacing most if not all of the standard port connectors on a PC. As with today's SCSI, one P1394 port on a PC allows you to connect multiple devices, up to 16 in current form.

The connector itself will cost manufacturers a few cents while the connectors alone for an RS-232C port can cost several dollars (and that can be a significant portion of the price of a peripheral or even PC). Moreover, a standard serial connector-that 25-pin D-shell connector-by itself is much too large for today's miniaturized systems. It can't fit a PCMCIA card by any stretch of the imagination or plastic work.

As less skilled people start tinkering with PCs and try linking them into multimedia systems, the simplified setup and wiring of P1394 should earn their praises. Today's high performance interface choice, SCSI, is about as friendly as a hungry bear awakened from hibernation. Although backed by strong technology, SCSI is a confusion of connectors, cables, terminators, and ID numbers. Wise folks find the best strategy is to stay out of the way. Where cabling a SCSI system means following rules more obscure than those of a fantasy adventure game, P1394 has exactly one wiring requirement: all P1394 devices in a system must connect without loops. There are no terminations to worry about, no different cable types like straight through and crossover, no cable length concerns, no identification numbers, and no connector genders to change. You simply plug one end of a P1394 cable into a jack on the back of the two devices you want to link. Most P1394 cables will have two or three jacks, so you can wire together elaborate webs. As long as no more than one circuit runs between any two P1394 devices, the system will work. It's even easier than a stereo system because there are no worries about input and output jacks.

Down deeper, however, P1394 is more complex. Instead of simply needing a UART, P1394 is a complex communications system with its own transfer protocol requiring new, application specific, integrated circuits. Although those initially will be expensive-estimated $15 per P1394 device-throughout the history of PCs, the cost of standard silicon circuits has plummeted while the cost of connectors continued to climb. Moreover, the current cost isn't entirely out of line with today's serial technology where a 16550AFN UART alone can cost $5 to $10. Just as the electrically more complex AT interface replaced older interfaces for hard disks, P1394 stands to step in place of the serial port.