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BEING MERRY WITH USB

by Tom Cantrell

Start ı Pride Before the Fall ı Universal Sales Booster ı The Mouse that Roared ı Wire Wars ı Kiss the Cook ı Sources and PDF

THE MOUSE THAT ROARED

Not that it was easy getting to this happy state of affairs. The origin of the USB we know and love goes back almost 10 years to something called ACCESS bus (see Photo 1), which I wrote about in my article, "The Ultimate Desk ACCESSory?" (Circuit Cellar 28) in 1992.

Photo 1ıItıs a bird, itıs a plane, itıs ACCESS bus. The ı92 standard couldıve been a contender but instead turned into USB, which we all should be thankful for

That article highlights just how far USB has come. Originally conceived by DEC and the then Signetics portion of what is now Philips, ACCESS bus was basically a tweak of the latter company's well-known I²C interface. Intended mainly to serve keyboards and mice (i.e., essentially a PC counterpart to Appleıs ADB), the pretensions of ACCESS bus were clearly limited by a humble 100-Kbps throughput spec.

Subsequently, Intel, Microsoft, and their minions jumped on the bandwagon. Actually, to make a long (and no doubt somewhat Machiavellian) story short, it would be more accurate to say they hijacked the bandwagon, and by ı95, ACCESS bus had morphed into USB. Many of the original ACCESS bus precepts were carried forward including power distribution over the cable, generic device classes, and hot plugging. The most visible changes were the connector (ACCESS bus used a phone-style modular connector) and much higher speeds (1.5 and 12 Mbps).

Even with all the heavyweights involved, it took USB years to get beyond the press release and developer conference phase. Two critical events in the gestation of USB were bundling by Intel on its own PC motherboards followed by delivery of decent software support in Windows 98. The pace of acceptance and growth of USB is all the more impressive given that, from the PC-customer-on-the-street point of view, itıs really only been on the shelf for a couple of years.

Itıs ironic, given the ADB-for-PC roots, that the success prospects were only reinforced by Appleıs adoption of USB for the iMacs. With blessings from the PC and Mac and a full lineup of standard peripherals on the market or in the pipeline, USB is poised to extend its reach even further.

I take special notice of the latest ColdFire micro, the MCF5272, from Motorola (see Figure 1). With practically every kind of communication channel under the sun built-in, inclusion of a USB port further signals mainstream adoption of the interface.

Figure 1ıYes, the MFC5272 has UART, SPI, and JTAG, but it also signals the arrival of Ethernet and USB as alternatives for blue-collar applications. (click to enlarge)

Itıs not merely the fact that the USB controller and transceiver are integrated thatıs important. Rather, unlike low-end, 8-bit mice and keyboard controllers, PC chipsets, and such, the ı5272 serves a much more diverse application space. Itıs not a USB-centric chip, which is exactly the point. Instead, the MCF5272 indicates that USB, along with Ethernet, will increasingly become a check-off item for general-purpose controllers, much the same as UARTs, SPI, I²C, and other serial interfaces have become standard issue.

Even on the desktop, look for the emergence of "legacy-free" PCs, which (like the iMac) finally starts to clean up the ludicrous jumble of ill-used serial, parallel, mouse, keyboard, game, and such ports. Itıs time to junk these senile interfaces once and for all. I strongly encourage all designers of any connected gadget to make the switch to USB or Ethernet for the good of users and your bottom line.

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