單片機(jī)基礎(chǔ)電氣工程及其自動(dòng)化畢業(yè)論文中英文翻譯-文庫(kù)吧資料
2024-12-01 09:13本頁(yè)面
【正文】 rial Input/Output Serial munication with terminal devices is a mon means of providing a link using a small number of lines. This sort of munication can also be exploited for interfacing special function chips or linking several microputers together. Both the mon asynchronous and synchronous munication schemes require protocols that provide framing (start and stop) information. This can be implemented as a hardware facility or U(S) ARP (Universal (synchronous) asynchronous receiver/transmitter) relieving the processor (and the applications programmer) of this lowlevel, timeconsuming, detail. It is merely necessary to select a baudrate and possibly other options (number of stop bits, parity, etc.) and load (or read from) the serial transmitter (or receiver) buffer. Serialization of the data in the data in the appropriate format is then handled by the hardware circuit. Timer/Counter Facilities Many applications of singlechip microputers require accurate evaluation of elapsed real time. This can be determined by careful assessment of the execution time of each branch in a program but this rapidly bees inefficient for all but the simplest programs. The preferred approach is to use a timer circuit that can independently count precise time increments and generate an interrupt after a preset time has elapsed. This type of timer is usually arranged to be preloadable with the required count. The timer then decrements this value producing an interrupt or setting a flag when the counter reaches zero. Better timers then have the ability to automatically reload the initial count value. This relieves the programmer of the responsibility of reloading the counter and assessing the elapsed time before the timer is restarted, which otherwise would be necessary if continuous precisely timed interrupts were required (as in a clock, 5 for example). Sometimes associated with a timer is an event counter. With this facility there is usually a special input pin, that can drive the counter directly. Timing Components The clock circuitry of most microputers requires only simple timing ponents. If maximum performance is required, a crys
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