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2024-09-04 07:45本頁(yè)面
【正文】 rts that because of the lack of a firm definition ,Omron39。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 justify DCS[distributed control system].With the starting price tags of chose products being relatively high, a programmable controller makes 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。re appropriate. one, he says, is where the size of the process control system that39。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。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。 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。 general manager, Siemens Energy amp。 in most a mechanism is provided to at least allow some flexibility of choosing which pins are outputs and which are inputs. This may apply to all or some of the ports. Some I/O lines are suitable for direct interfacing to, for example, fluorescent displays, or can provide sufficient current to make interfacing other ponents straightforward. Some devices allow an I/O port to be configured as a system bus to allow offchip memory and I/O expansion. This facility is potentially useful as a product range develops, since successive enhancements may bee too big for onchip memory and it is undesirable not to build on the existing software base.Serial input/output .Serial munication with terminal devices is 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 synchronous munication schemes require protocols that provide framing (start and stop) information .This can be implemented as a hardware facility or U(S)ART(Universal(synchronous) 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 single
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