Embedded Systems December 2000 Vol13_13

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-= nel thal is used fo r this setting. The user may have the option of changing it, but guessing defaults in this way can reduce the amount of interactions that the user has to make. The principle of using a piece of device o utpul as a piece of user input i kn own as equal opportuni ty.2 1n win- dowing sys tems, the abilily to cut text from o ne window and paste it into another is quite common. Many sys- lems limil the usefulness of this fea- lure by nOl allowing it fo r all output. I occasionally get an error message that J wish to e-mail to the system adminis- u"ation team. ] am fo rced to retype the message because my computer will not allow me to copy il and pasle it into my e-mail window. ]f data is already avail- abl e, do nOl fo rce the user to ente r it again. A number of other examples of equal opportuni ty are available on my Web site. Multiple paths If your in te rface provides more than o ne way to perform a function, ask yourself "]s there a reason for each path ?" You sho uld ask this question, because the user wi II. If one way is slow but o bvious, and another is quick but only likely lO be known by th e expert user, then each has a purpose. The quick method is a shortcut. In other cases it may be useful to have a feature available from a number of different modes, to reduce the need for the u er to change modes to find this pop- ular feature. However, if th e alte rn atives are arbi trary, the user may assume that the re is some diffe re nce in th e resul t-perhaps some side effect that he never noticed while using this fea- lure" Thi may lead to user discomfort since he believes that there i some- lhing about the interface th at he does not understand. Migrating from mechanical controls Having comple te software control over the inlerface removes the use r by one more level from the mechani cs of lhe device itself. If software interprets all user inputs and then generates sig- nals to control the device based on those inputs, you have a fly-by-wire sys- tem. This may affect the use." in a num- ber of subtle ways. A dial connected to a potentiometer may have had a loga- rithmic relationship witll tlle voltage output. The software control system may make that relationship linear. Analog needles showing values are usual ly damped to prevent oscillations of tlle needle tllat would make it diffi- cult to read the value indicated. A real- time graph of the value may show a lot of valiabili ty that was previously not 'iii '5 Ours Microcontroller analog emulation. We measure analog at the pin. We put the emulation circui try right o n the COP8FLASH chi p. This allows you to solder a chip ample directly into your target board. The re ult? 100% precise analog emulation with no noise probl ms, no voltage offset problems, n unwanted inducta nce or ca pacitance. And no distortion at all . Why don't more chip makers emulate in this fas hion? Sometimes things this simple in concept are a bit trickier in executio n. And that's where ational's experience makes all the difference. To lea rn more about the expanding COP8FLA H microcontroller portfoliO, visit us at copSflash The all new COPSFLASH family is here. ~National P Semiconductor 1\.111(1);11 ~lllicond\lCIOr Corpor.lllon, 1000. :'\:\11011:11 ~rnjconduClor ,Inc! t9 ;m: rl.'w ... ' t:r(.:d 1r:l(lcm:lrk!> of ~.lI i(Jn, 11 SCmkondu<.Ior Corpor.l l ion. Al l nght.-. -oo. Embedded Systems Programming DECEMBER 2000 67

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