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 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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