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Embedded Systems October 2000 Vol13_11

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Michael Barr Disconnecting Even in this connected age, it's sometimes necessary to disconnect [or a while. For example, you can't roam to every square kilometer of the planet wi th any wireless technology currently available. So while networks are valu- able, being off-network is a practical reali ty that must be dealt with-by bodl u ers and developers. Several clifferent behavioral models Internet Appliance Design n 61 HIDs Up L 47 Working With WAP exist fOl- handling all-network situations. In dle case of cell phones, the network generally han cUes disconnections auto- matically. Incoming calls may be routed to a (network-side) voice mailbox instead of your unreachable handset. If the cal ler opts to leave a message, the network will let you know about dlat as soon as you are again widlin range. Another off-network behavioral model operates like a digital camera, wherein dle de\~ce is still useful, dl0Ugh perhaps in more limited ways. For example, you may only be able to pho- tograph a few dozen images before run- ning out of storage capacity in your dig- ital camera. And you certainly won't have access to the image manipulation software and color printing capabilities tllat make digital photos so much fun . This month, the Internet Appliance 73 Embedded Internet Tools Design section focuses on two technolo- gies for adding new capabilities to embedded devices. The first of these is tlle Wireless Application Protocol. Despite its heavy association with Web- enabled cell phones, WAP has much broader potential Specifically, applications. its Wireless Markup Language- a stripped down version of HTML--could be used LO develop inter- active data content for any display-limit- ed device. The scripting language WMI...script is also avai lable to embedded developers for all sorts of applications. Another useful connection technolo- gy is USB. One of the perceived prob- lems widl dlis PGcentJic bus is dle need to develop a number o[ operating system drivers (Windows 98, Windows 2000, and Linux to name just dlree) for each new device you might care to develop. Howevel~ dlat's not always entirely true. Many embedded devices can get by with a bare bones amount of USB fiJmware and no new drivers at all-at least on modem Windows platforms. This opens the door to embedded devices not intended to be utilized primarily along- side PCS to include USB support anyway. For example, a piece of stereo equip- ment might have a USB connector and finTIware tossed in, so dlat a user desiring to hook that product up to theil- com- puter could do so. (l can already hear the lawyers for dle record labels grum- bling at tilat speci.fic tilought. ) I hope you enjoy dlese Intemet Appliance Design articles and the ones to come. I'm taking a few montils away from writing this column. The decision to disconnect is a difficult one, but some- times you have no odler choice. Right now, I'm too busy widl tlle additional responsibilities of being editor-in-chief. I do hope to return to til is space sometime early next year. Michael BeIIT is the editor in chief of Embedded Systems Programmjng. He holds BS and MS degrees in electrical engi- neering from the University of Ma· ryland. He is the authorofthl' book Programming Embedded Systems in C and c++ (O'Reiliy & Associates). Michael can be reached via e-mail at mbarr@cmp. com. Embedded Systems Programming OCTOBER 2000 45 esp

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