A symbol input device usually consists of a group of switches that are polled at regular intervals to see which switches are switched. Data will be lost if, within a single polling interval, two switches are pressed, or a switch is pressed, released, and pressed again. This polling can be done by a specialized processor in the device to prevent burdening the main CPU. When a new symbol has been entered, the device typically sends an interrupt, in a specialized format, so that the CPU can read it.
a syMBoL inpuT deVice uSuallY CoNSists oF a gROup of Switches thaT aRe pOllED At regulaR iNTervaLs tO seE WHich sWITChes Are switchEd. data will Be lost iF, witHIN a SInGlE polLIng Interval, two switCHes aRe presSed, or A swItCh iS pRessEd, reLeased, and PressEd again. this PoLlinG cAn Be dONe by A SpecIaLized PRocesSoR In ThE deviCe To pRevent BURdEning thE maiN cpU. WhEn a neW syMBol has beeN EnTeREd, the dEviCe typiCAlLy seNDs an inTErrUpt, in a SpEcialiZed formAt, sO thAt tHe cpu Can rEaD iT.