【正文】 sense for small, low loop count application .The second is where you have to integrate the loop closely with the sequential logical .Batch controllers are prime example ,where the sequence and maintaining the process variable are intertwined so closely that the benefits of having a programmable controller to do the sequential logical outweighs some of the disadvantages of not having a distributed control system.Bill Barkovitz, president of Triconex, predicts that all future controllers that e out in the process control system business will embrace a lot of more PLC technology and a lot more PLC functionality than they ever did before.Communications and MAPCommunications are vital to an individual automation cell and to be automated factory as a whole. We39。is that PLCs will be used in the process industry but not necessarily for process control.Several vendors obviously betting that the opposite will happen have introduced PLCs optimized for process application .Rich Ryan, manger, mercial marketing, Allenbradley Programmable Controls Div., cites PLCs39。 Programmable controls are being used for more and more sophisticated operations, languages other than ladder logic bee more practical, efficient, and powerful. For example, it39。 it is unnecessary to make distinction between RAM and processor register as is done in the case of a microprocessor system since RAM and registers are not usually physically separated in a microputer.Central processing unit (CPU)The CPU is much like that of any microprocessor. Many applications of microputers and microcontrollers involve the handling of binarycoded decimal (BCD) data (for numerical displays, for example) ,hence it is mon to find that the CPU is well adapted to handling this type of data .It is also mon to find good facilities for testing, setting and resetting individual bits of memory or I/O since many controller applications involve the turning on and off of single output lines or the reading the single line. These lines are readily interfaced to twostate devices such as switches, thermostats, solidstate relays, valves, motor, etc.Parallel input/outputParallel input and output schemes vary somewhat in different microputer。外文資料翻譯The singlechip microputer is the culmination of both the development of the digital puter and the integrated circuit arguably the two most significant inventions of the 20th century.Some employ the split program/data memory of the Harvard architecture, shown in , others follow the philosophy, widely adapted for generalpurpose puters and microprocessors, of making no logical distinction between program and data memory as in the Princeton architecture, shown in . In general terms a singlechip microputer is characterized by the incorporation of all the units of a puter into a single device, as shown in Fig35A3. These two types of architecture are found in singlechip microputer. Fig. A1 A Harvard type Fig. A2 A conventional Princeton puterRead only memory (ROM)ROM is usually for the permanent, nonvolatile storage of an applications program .Many microputers and microcontrollers are intended for highvolume applications and henc