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Embedded Systems December 2000 Vol13_13

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I: " Having moved from an analog device to a di gital di splay, many inte rface fa ll into the trap of giving the use r fa r mo re precision than they require. There is little value in telling users that they have enough fuel fo r anothe r 3l.7 miles, sin ce th ey would be foolish to wait until th e last 0.7 of a mile befo re I -efuel- ing. The vagueness of th e needle in this case is an advantage. The needle says "I don' t know exactly how much furthe r you can go, and we are not a t th e panic stage yet, but if you see a gas sta tion, you may as well stop." Sin ce no one can know exactly how many more miles th e fuel will las t, this information may be more appro- priate than 3l.7 miles . The more precise value may lure th e driver into a false se nse of securi ty. A tempting alternative may be to pre- sent th e drive r with a I -ange of val- ues. However, I do not think many drivers would appreciate a display tha t a id 3l.7 mil es ±lO%. Remem be r, th ey are not all engi- neers and may not be exposed to th e concept of to le rance every day. If tlle tan k is low on fu el, the sensi- ble thing to do is fill up at the next opportuni ty. eedle gauges are noto- riously non-linear, but drivers rarely complain. The designer may do well to copy the functionality of the nee- d le. This will be less threatening for the new user because he can relate easily to his pa t expe rience with the needle di splay. An inte rface con- trolled from software could control a needl e, or use a bar graph on an LCD displ ay, or a bar graph made up of a numbe r of LEDs. Which appearance is chosen i less significant than the functionality attached to it. Users will quickly adapt to a new appearance, but users take longer to adapt to chan ges in fun ctionality. esp Niall MurjJhy has been writing software fOT user interfacps and medical systems f or ten yeaTS. He is the authoT of Front Panel: Designing Softwa re for Embedded User Inte rfaces (R&D Books). Mwphy's WHh COPSFLASH, in-system programming is software controlled and all support circuHry is integrated on-chip. For true in-system programming, COP8FLASH is your I est choice. It integrates high-voltage circui try that UI ports fl ash programming across the full 2.7 - 5.5V operating range. Switch bet\veen norma I operating mode a nd flash programming mode easil y. The re's no external reset or dedicated control Signal req uired - it's entirely software con troll d. And beca use our ]SP cod resides in a fa il-safe boot-ROM, if you lose power, your code is still on-chi p. You simply sta rt over. 0 for designs that won't unravel, get the chip without the loose ends. To learn more about the xpanding COP8FLASH microcontroller portfolio, visit us at www.nationa1.com/ copSflash tmining and consulting business is based in Galway, Ireland. He welcomes feedback and can be reached at nrnurj)hy@jJanel- soft . corn. References 1. Thimbleby, Harold. User Interface Design. New York City: ACM Press, 1990. 2. Equal Opportunity Tutorial available at www.pane/soft.comltuCequa/. Resources Niall Murphy's on- line list of usability resources is available at www.pane/soft. coml usab/e.htm. 'iii GI '5 Ours The all new COPSFLASH family is here. P Semiconductor ... '1 National t , "lallolul ScIl1tC:onductor Co rporat ion. 2000. ':uion;11 "'I.'micnnduclor and tiJ arc r .... J(I~Il.·r(.-d tr.lcit.'lll!lrk!> of '\:ll ion.11 X'mi('onducror Corporallon All right.'> rL':.crwci Embedded Systems Programming DECEMBER 2000 69

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