單片機畢業(yè)外文翻譯-wenkub
2023-01-31 11:06:53 本頁面
【正文】 asynchronous receiver/transmitter) relieving the processor (and the applications programmer) of this lowlevel, timeconsuming, detail. t is merely necessary to selected 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 appropriate format is then handled by the hardware circuit.Timing/counter facilities Many application 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 simplest programs .The preferred approach is to use 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 reloadable 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 elapsed time before the timer restarted ,which otherwise wound be necessary if continuous precisely timed interrupts were required (as in a clock ,for example).Sometimes associated with timer is an event counter. With this facility there is usually a special input pin , that can drive the counter directly. Timing ponents The clock circuitry of most microputers requires only simple timing ponents. If maximum performance is required, a crystal must be used to ensure the maximum clock frequency is approached but not exceeded. Many clock circuits also work with a resistor and capacitor as lowcost timing ponents or can be driven from an external source. This latter arrangement is useful is external synchronization of the microputer is required. Programming languages Higher level PLC programming languages have been around for some time, but lately their popularity has mushrooming. As Raymond Leveille, vice president amp。 there can still be a significant saving in I/O and other chips pared to a conventional microprocessor based circuit. More exact replacement for ROM devices can be obtained in the form of variants with 39。piggyback39。 general manager, Siemens Energy amp。s increasing interest in languages like C and BASIC.PLCs in process controlThus far, PLCs have not been used extensively for continuous process control .Will this continue? The feeling that I39。re appropriate. one, he says, is where the size of the process control system that39。t appear immediately .Says Larry Komarek: Right now, MAP is still a moving target for the manufacturers, a specification that is not final .Presently, for example. people are introducing products to meet the . products will be obsolete when the new standard for is introduced.Because of this, many PLC vendors are holding off on full MAP implementations. Omron, for example, has an ongoing MAPpatibility program。t yet talk to MAP.Since it39。t begin selling universal I/O system from other vendor. if we start selling that kind of pro
環(huán)評公示相關(guān)推薦
鄂ICP備17016276號-1