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PLC technique discussion and future development Along with the development of the ages, the technique that is nowadays is also gradually perfect, the competition plays more strong; the operation that list depends the artificial produce practice, automate brought the tremendous convenience and the product quantities for people up of assurance, also eased the personnel's labor strength, reduce the establishment on the personnel. The target control of the in many complicated production lines, whole and excellent turn, the best decision etc., well-trained operation work, technical personnel or expert, governor but can judge and operate easily, can acquire the satisfied result. The research target of the artificial intelligence makes use of the calculator exactly to carry out, imitate these intelligences behavior, moderating the work through person's brain and calculators, with the mode that person's machine combine, for resolve the very complicated problem to look for the best path
We come in sight of the control that links after the electric appliances in various situation, that is already the that time generation past, now of after use in the mold a perhaps simple equipments of grass-roots control that the electric appliances can do for the low level only; And the PLC emergence also became the epoch-making topic, adding the vivid software control through a very and stable : The electrical engineering teacher already no longer electric that the button switch or the importation of the sensors order to link the PLC up can solve problem, pass to output to order the conjunction contact machine or control the start equipments of the big power after the electric appliances, but the exportation equipments direct conjunction of the small power can.
PLC internal containment I O for expand of exterior to connect a people's address and saving machine three big pieces to constitute, CPU core is from an or many is tired to add the machine to constitute, mathematics that they ability, and can read the procedure save the contents of the machine to drive the ; The I O add inner part is tired the input and output system of the machine and exterior link, and deposit the related data into the procedure saving machine or data saving machine; The saving machine can deposit the data that the I O input in the saving machine, and in work adjusting to become tired to add the machine and I Os to connect, saving machine separately saving machine RAM of the procedure saving machine ROM and dates, the ROM can do deposit of the data permanence in the saving machine, but RAM only for the CPU computes the temporary calculation usage of its service life and the work situation bad, these all problems to come to internal resources of make use of the PLC to strengthen the control ability of the equipments for us, make our equipments more gentle.
PLC language is not we imagine of edit collected materials the language or language of Cs to carry on weaving the distance, but the trapezoid diagram that
the adoption is original after the electric appliances to control, make the electrical engineering teacher while weaving to write the procedure very easy comprehended the PLC language, and a lot of non- electricity professional also very quickly know and go deep into to the PLC.
Is PLC one of the advantage above and only, this is also one part that the people comprehend more and easily, in a lot of equipments, the people error perhaps you can still accept; But lead even is a fatal error greatly is what we can't is tolerant of. New technique always for bringing more safe and convenient operation for us, make we a lot of problems for face on sweep but light, do you understand the HMI? Says the HMI -machine interface you knew, and it combines with the PLC to our larger space.
HMI the control not only is reduced the control press button, increase the vivid of the control, more main of it is can sequence of, and at can the change data input to output the feedback with data, control in the temperature curve of imitate but also can keep the manifestation of view to come out. And can write the function one's power, the one who make operate reduces the otiose error. Currently the HMI factory is also more and more, the function is also more and more strong, the price is also more and more low, and the noodles of the usage are wide more and more. The HMI foreground can say that think ° to be good very.
At a lot of situations, the list is a smooth movement that can't guarantee the equipments by the control of the single machine, but pass the information exchanges of the equipments and equipments to attain the result that we want. For example fore pack and the examination of the empress work preface, we will arrive wrapping information feedback to examine the place, and examine the information of the place to also want the feedback to packing. Pass the information share thus to make both the chain connect, becoming a total body, the match of your that thus make is more close, at each other attain to reflect the result that mutually flick.
The PLC correspondence PLCs, can pass the communication of the information and the share of the dates to guarantee that of the equipments moderates mutually, the result that arrive already to repair with each other. Data conversion the adoption RS232 between PLC connect to come to the transmission data, but the RS232 pick up a people and can guarantee 10 meters only of deliver the distance, if in the distance of 1000 meters we can pass the RS485 to carry on the correspondence, the longer distance can pass the MODEL only to carry on deliver.
The PLC data transmission is just to be called a form to it in a piece of and continuous address that the data of the inner part delivers the other party, we, the PLC of the other party passes to read data in the watch to carry on the operation. If the data that data in the watch is a to establish generally, that is just
the general data transmission, for example today of oil price rise, I want to deliver the price of the oil price to lose the oil ally on board, that is the share of the data; But take data in the watch for an instruction procedure that controls the PLC, that work that you imagine, you will draw up for it the form that a procedure combine with the data sends out to pass by.
The form that information transport contain single work, the send out only, but a can receive only, for example a spy receive the designation of the superior only, but can't give the superior reply; A work of send out similar to accept the data, but can't send out and accept at the same time, for example when you make a phone call is to can't answer the phone, the other party also; But whole pair works is both can send out and accept the data, and can send out and accept at the same time. Be like the Internet is a typical example.
The process that information transport also synchronous meaning lie in sending out the data, is also the data signal and the clock signals to be carry on by the CPU to send out at the same time, this needs to all want the specialized clock signal each other to carry on the transmission and connect to send, and is constrained, the characteristics of this kind of method lies in its speed very quick, but correspond work time of take up the CPU and also want to be long oppositely, at the same time the technique difficulty also very big. Its request lies in canting error margins in a dates deliver, otherwise the whole piece according to compare the occurrence mistake, this on the some appropriative equipments, be like the appropriative medical treatment equipments, the numerical signal equipments...etc., in compare the one data deliver, its result is very good.
And the different step is an application the most extensive, this receive benefit in it of technique difficulty is opposite and want to be small, at the same time not need to prepare the specialized clock signal, its characteristics to lie in, its data is partition, the long-lost send out and accept, be the CPU is too busy of time can grind to a stop sex to work, also reduced the difficulty on the pass the examination of the data to observe whether the data that we send out and eight efficacies method etc., can use to the discriminator.
A line of transmission of the information contains a string of and combine the cent of: The usual PLC is 8 machines, certainly also be an at the time of sending out the data a send out to the other party, also can be 88 send out the data to the other party, an and 8 differentiations are also the as that we say to send out the data and combine sends out the data. A speed is more and slowly, but as long as 2 or three lines can solve problem, and can use the telephone line to carry on the long range control. But combine the ocular transmission speed is very quick of, it is a string of ocular of 25600%, occupy the advantage in the short distance, the in view of the fact TTL electricity is even, being limited by the scope of one meter generally, it combine unwell used for the data transmission of the long pull, thus the cost is too expensive.
Under a lot of circumstances we are total to like to adopt the string to combine the conversion chip to carry on deliver, under this kind of circumstance not need us to carry on to deposited the machine to establish too and complicatedly, but carry on the data exchanges through the data transmission instruction directly, but is not a very viable way in the correspondence, because the PLC of the other party must wait for your data exportation at the time of sending out the data, it can't do other works.
When you are reading the book, you door, you stop to start up of affair, open the door and combine to continue with the one who knock on door a dialogue, the telephone of this time rang, you signal overdo come together knock on door to , after dialogue complete, you continue again to see your book, this kind of circumstance we are called the interruption to it, it .Its characteristics lie in us and may meet the urgently abrupt affairs in the operation process of the equipments, we want to stop to start immediately up of work, the whereabouts manages the more important affair, this kind of circumstance is we usually meet of, PLC while carry out urgent mission, total will keep the current appearance first, for example the address of the procedure, CPU of tired add the machine data etc., be like to stick down which the book that we see is when we open the door the page or simply make a mark, because we treat and would still need to continue immediately after book of see the behind. The CPU always does the affair that should do according to our will, but your mistake of give it an affair, it also would be same to do, this we must notice.
The interruption is not only a, sometimes existing jointly with the of the to also became to break off the set. The Class that certainly break off is relevant according to various resources of CPU with internal PLC, also following a .
The contents that break off of send out and accept the interruption and settle and the clock that count break off, still etc., they enriched the CPU to respond to the category while orders of the interruption completely also, we do a very small example to explain.
Each equipment always will not forget a button, it also is at we meet the urgent circumstance use of, which is nasty to stop the button. When we meet the Human body trouble and surprised circumstances we as long as press it, the machine stops all operations immediately, and wait for processing the over surprised empress recover the operation again. Nasty stop the internal I O of the internal CPU of the button conjunction PLC to connect up, be to press button an exterior to trigger signal for CPU, the CPU carries on to the I O to examine again, being to confirm to the spot breaks off procedure counts the machine turn the the procedure to go to also, be exterior interruption procedure processing complete, the procedure counts the machine to return the main procedure to continue to work. Have 1:00 can what to explain is we generally would nasty stop the button of exterior break off to rise to the tallest Class, thus guarantee the safety.
When we are work a work piece, giving the PLC a signal, counting PLC inner part the machine add 1 to compute us for a day of workload, a count the machine and can solve problem in brief, certainly they also can keep the data under the condition of dropping the electricity, urging the data not to throw to lose, this is also what we that the all aspects tiny second class, for example the bar code scanner is scanning the data continuously, calculating count. It at the PLC carries out the procedure once discover that the , will let go of the work on the explains the procedure circulate. The PLC also the inner part of PLC, we can establish time that a procedure of WDT circulate, being to appear the procedure to jump to turn the mistake in the procedure movement process or the procedure is busy, movement time of the procedure exceeds WDT constitution time, the CPU turn but the WDT reset the appearance. The procedure restarts the movement, but will not carry on the breakage to the interruption.
The PLC development the share easily. A state software can pass all se picture of keep the view to carries on the control, and cans pass the Internet to carry on the control in the foreign land, the blast-off that is like the absolute being boat No.5 is to adopt this kind of way to make airship go up the sky.
The development of the . The PLC emergence , coming to the continuous development PLC technique, push it toward efficient and flexible control system design.
The programmable logic controller's (PLC's) ability to support a range of communication methods makes it an ideal control and data acquisition device for a wide variety of industrial automation and facility control applications. However, there is some confusion because so many possibilities exist. To , let's list what communications are available and when they would be best applied.
To understand the PLC's communications versatility, let's first define the terms used in describing the various systems.
ASCII: This stands for "American Standard Code for Information Interchange." As shown in Fig. 1, when the letter "A" is transmitted, for instance, it's automatically coded as "65" by the sending equipment. The receiving equipment translates the "65" back to the letter "A." Thus, different devices can communicate with each other as long as both use ASCII code.
ASCII module: This intelligent PLC module is used for connecting PLCs to other devices also capable of communicating using ASCII code as a vehicle.
Bus topology: This is a linear local area network (LAN) arrangement, as shown in Fig. 2A, in which individual nodes are tapped into a main communications cable at a single point and broadcast messages. These messages travel in both directions on the bus from the point of connection until they are dissipated by terminators at each end of the bus.
CPU: This stands for "central processing unit," which actually is that part of a computer, PLC, or other intelligent device where arithmetic and logical operations are performed and instructions are decoded and executed.
Daisy chain: This is a description of the connection of individual devices in a PLC network, where, as shown in Fig. 3, each device is connected to the next and communications signals pass from one unit to the next in a sequential fashion.
Distributed control: This is an automation concept in which portions of an automated system are controlled by separate controllers, which are located in close proximity to their area of direct control (control is decentralized and spread out over the system).
Host computer: This is a computer that's used to transfer data to, or receive data from, a PLC in a PLCcomputer network.
Intelligent device: This term describes any device equipped with its own CPU.
IO: This stands for "inputs and outputs," which are modules that external device.
Kbps: This stands for "thousand bits per second," which is a rate of measure for electronic data transfer.
Mbps: This stands for "million bits per second."
Node: This term is applied to any one of the positions or stations in a network. Each node incorporates a device that can communicate with all other devices on the network.
Protocol: The definition of on a network.
Ring topology. This is a LAN arrangement, as shown in Fig. 2C, in which each node is connected to two other nodes, resulting in a continuous, closed, circular path or loop for messages to circulate, usually in one direction. Some ring topologies if the main cable is severed.
RS232. This is an IEEE standard for serial communications that describes specific wiring connections, voltage levels, and other operating parameters for electronic data communications. There also are several other RS standards defined.
Serial: This is an electronic data transfer scheme in which information is transmitted one bit at a time.
Serial port: This the communications access point on a device that is set up
for serial communications.
Star topology. This is a LAN arrangement in which, as shown in Fig. 2B, nodes are connected to one another through a central be active or passive. An active a LAN in relation to one another.
Transparent: This term describes automatic events or processes built into a system that require no special programming or prompting from an operator.
Now that we're familiar with these terms, let's see describing the available PLC network options.
PLC network options
PLC networks provide you with a variety of networking options to meet specific control and communications requirements. Typical options include remote IO, peer-to-peer, and provide reliable and cost-effective communications between as few as two or as many as several ASCII interface for the connection(s), along with considerable work with software.
Remote I0 systems
A remote IO configuration, as shown in Fig. 4A, be described as a "master-and-slave" configuration, allows many distant digital and analog points to be controlled by a single PLC. Typically, remote IOs are connected to the CPU via twisted pair or fiber optic cables.
Remote IO configurations can be extremely cost-effective control solutions where only a few IO points are needed in widely separated areas. In this situation, it's not always necessary, or practical for that matter, to be used in acquiring data from remote plant or facility locations. Information such as cycle times, counts, duration or events, etc. then can be sent back to the PLC for maintenance and management reporting.
In a remote IO configuration, the master controller polls the slaved IO for its current IO status. The remote IO system responds, and the master PLC then signals the remote IO to change the state of outputs as dictated by the control program in the PLC's memory. This entire cycle occurs in Fig. 4B, enhance reliability by decentralizing the control functions without sacrificing coordinated control. In this type of network, numerous PLCs are connected to one another in a daisy-chain fashion, and a common memory table is duplicated in the memory of each. In this way, when any PLC writes data to this memory area, the information is automatically transferred to all other PLCs in the network. They then can use this information in their own operating programs.
With peer-to-peer networks, each PLC in the network is responsible for its own control site and only needs to be programmed for its own area of
responsibility. This aspect of the network significantly reduces programming and debugging complexity; because all communications occur transparently to the user, communications programming is reduced to simple read-and-write statements.
In a peer-to-peer system, there's no master PLC. However, it's possible to designate one of the PLCs as a master for use as a type of group controller. This PLC then can be used to accept input information from an operator input terminal, for example, sending all the necessary parameters to other PLCs and coordinating the sequencing of various events.
Host computer links
PLCs also can be connected with computers or other intelligent devices. In fact, most PLCs, from the small to the very large, can be directly connected to a computer or part of a multi drop of computer and controller maximizes the capabilities of the PLC, for control and data acquisition, as well as the computer, for data processing, documentation, and operator interface.
In a PLCcomputer network, as shown in Fig. 4C, all communications are initiated by the a daisy-chain fashion. This computer individually addresses each of its networked PLCs and asks for specific information. The addressed PLC then sends this information to the computer for storage and further analysis. This cycle occurs aid in programming PLCs; powerful programming and documentation software is available for program development. Programs then can be written on the computer in relay ladder logic and downloaded into the PLC. In this way, you can create, modify, debug, and monitor PLC programs via a computer terminal.
In addition to must interface with other devices, such as operator interface terminals for large security and building management systems. Although many intelligent devices can communicate directly with PLCs via conventional RS232C ports and serial ASCII code, some don't fixed formats. It's the PLC programmer's responsibility to provide the necessary software interface.
The easiest way to provide such an interface to fixed-format intelligent devices is to use an ASCIIBASIC module on the PLC. This module is essentially a small computer that plugs into the bus of the PLC. Equipped with RS232 ports and programmed in BASIC, the module easily can functions, programming sequences, "number crunching," report and display generation, and other requirements.
Access, protocol, and modulation functions of LANs
By using standard interfaces and protocols, LANs allow a mix of devices (PLCs, PCs, mainframe computers, operator interface terminals, etc.) from many different vendors to communicate with others on the network.
Access: A LAN's access method prevents the occurrence of more than one message on the network at a time. There are two common access methods.
Collision detection is where the nodes "listen" to the network and transmit only if there are no other messages on the network. If two nodes transmit simultaneously, the collision is detected and both nodes retransmit until their messages get through properly.
Token passing allows each node to transmit only if it's in possession of a special electronic message called a token. The token is passed from node to node, allowing each an opportunity to transmit without interference. Tokens usually for a long period of time.
Protocol: Network protocols define the way messages are arranged and coded for transmission on the LAN. The following are two common types.
Proprietary protocols are unique message arrangements and coding developed by a specific vendor for use with that vendor's product only.
Open protocols are based on industry standards such as TCPIP or ISOOSI models and are openly published.
Modulation: Network modulation refers to the way messages are encoded for transmission over a cable. The two most common types are broadband and baseband.
Network transmission interfaces
The vast majority of PLC communications is done via RS232C and twisted pair cables. Most PLCs RS232 port and are capable of speed is 19.2 Kbps.
The distance and data transmission rates are standards for the various interfaces. Their actual performance is a function of the driving devices and varies significantly between manufacturers. As such, you should consult the manufacturer's specifications for actual distance and data transmission rate capabilities.
The only real limitation on RS232C is the 50-ft recommended distance between devices. While RS232C installations often can achieve cabling distances greater than this, the "unbalanced" design of the interface results in a greater susceptibility to surrounding electrical noise and reduced data integrity. This is particularly true where electromagnetic interference (EMI) and radio-frequency interference (RFI) are known to exist.
When longer transmission distances are needed, RS422 is a better choice. Unlike the RS232C interface, RS422 is "balanced." Each of its primary signals consists of two wires that are always at opposite logic levels, with respect to
signal ground. As a result, the interface can achieve longer transmission distance (4000 ft) and rates (up to 90 Kbps). In shorter runs (less than 50 ft), data transfer can reach 10 Mbps.
Fiber optic communications are gaining greater acceptance and are being used in more and more installations. Fiber optic cable is virtually impervious to span extremely long distances and transmit data at very some LAN systems, these links can transmit at relatively long distances before requiring a repeater. When repeaters are used, virtually unlimited distances can be achieved.
中文翻译
可编程控制器技术讨论与未来发展
随着时代的发展,当今的技术也日趋完善、竞争愈演愈烈;单靠人工的操作已不能满足于目前的制造业前景,也无法保证更高质量的要求和高新技术企业的形象.
人们在生产实践中看到,自动化给人们带来了极大的便利和产品质量上的保证,同时也减轻了人员的劳动强度,减少了人员上的编制.在许多复杂的生产过程中难以实现的目标控制、整体优化、最佳决策等,熟练的操作工、技术人员或专家、管理者却能够容易判断和操作,可以获得满意的效果.人工智能的研究目标正是利用计算机来实现、模拟这些智能行为,通过人脑与计算机协调工作,以人机结合的模式,为解决十分复杂的问题寻找最佳的途径
我们在各种场合看到了继电器连接的控制，那已经是时代的过去，如今的继电器只能作为低端的基层控制模块或者简单的设备中使用到；而PLC的出现也成为了划时代的主题，通过极其稳定的硬件穿插灵活的软件控制，使得自动化走向了新的高潮。
PLC的最大特点在于：电气工程师已不再电气的硬件上花费太多的心计，只要将按钮开关或感应器的输入点连接到PLC的输入点上就能解决问题，通过输出点连接接触器或继电器来控制大功率的启动设备，而小功率的输出设备直接连接就可以。
PLC的内部包含了具有中央处理器的CPU，并带有外部IO口扩展的IO接口地址和存储器三大块组成，CPU的核心是由一个或者多个累加器组成，它们具有逻辑的数学运算能力，并能读取程序存储器的内容通过计算后去驱动相应的存储器和IO接口；IO口将内部累加器和外部的输入和输出系统连接起来，并将相关的数据存入程序存储器或者数据存储器中；存储器可以将IO口输入的数据存入存储器中，并在工作时调转到累加器和IO接口上，存储器分程序存储器ROM 和数据存储器RAM,ROM可以将数据永久的存入存储器中，而RAM只能作为CPU 计算时临时计算使用的缓冲空间。
PLC的抗干扰是极其优秀的，我们根本不用去关心它的使用寿命和工作场合的恶劣，这些所有的问题已不再成为我们失败的主题，而留给我们的是关心如
何来利用PLC的内部资源为我们加强设备的控制能力，使我们的设备更加的柔性。
PLC的语言并不是我们所想象的汇编语言或C语言来进行编程，而是采用原有的继电器控制的梯形图，使得电气工程师在编写程序时很容易就理解了PLC 的语言，而且很多的非电气专业人士也对PLC很快认识并深入。
以上仅仅是PLC的优点之一，这也是人们比较容易理解的一部分，在很多的设备中，人们已不再希望看到太多的控制按钮，它们不但容易损坏而且极易产生人为的失误，小的并不是主要的失误也许你还能够接受；但过大的甚至是致命的失误是我们无法容忍的。新的技术总是为了给我们带来更安全和便捷的操作，使得我们面临的一大堆问题一扫而光，你有了解过HMI吗？这里说HMI 你根本不清楚它是什么，也没有兴趣了解，换一个中文把它说明为触摸屏或者人机界面你就知道了，它和PLC的结合给了我们更大的空间。
HMI控制不仅仅是减少了控制按钮，增加控制的灵活性，更主要的它是可顺序性的，而且在能够改变数据输入和数据输出反馈，在温度控制曲线的模拟也能直观的显示出来。并且能够通过编写功能帮助程序来提供各种力所能及的帮助，使得操作者减少不必要的失误。HMI的厂商目前也越来越多，功能也越来越强，价格也越来越低，使用的面越来越广。HMI的前景可以说十分的看好。
在很多场合，单靠单机的控制是无法保证设备的顺畅运行，而通过设备与设备的信息交流达到我们想要的效果。比如在前包装和后工序的检测，我们就要将包装的信息反馈到检测处，而检测处的信息也要反馈到包装来。这样通过信息共享来使得两者之间链接起来，形成一个共体，从而使的两者间的配合更加的紧密，在彼此间达到映影相挥的效果。
PLC的通信已经愈来愈体现它的价值，在PLC与PLC之间的通信，能够通过信息的沟通和数据的共享来保证设备之间的相互协调，已达到互补的效果。PLC 之间的数据转换采用RS232接口来传送数据，而RS232接口只能保证10米的传输距离，如果在1000米的距离内我们可以通过RS485来进行通信，更长的距离只能通过MODEL来进行传输。
PLC的数据传送只是将内部的数据传送到对方的一块连续的地址中，我们把它称为一个表，对方的PLC通过读取表中的数据来进行操作。如果表中的数据
是一个一般设置的数据的话，那只是一般的数据传送，比如今天的油价上升了，我要把油价的价格传送到所有的输油机上，那就是数据的共享；而当表中的数据是一段控制PLC的指令程序，那就很有难度了，比如你要控制一台机器人来按你想象的动作工作，你会给它编制一段程序并以数据的形式发送过去。
信息输送的形式有单工位、半双工位和全双工位的分别。单工位的意义也就是说两者之间，一个只能发送，而一个只能接收，比如一个特务他只能接收上司的指示，而无法给上司回复；半双工位也就是两个能都能发送和接受数据，但不能同时发送和接受，比如你打电话时是不能接电话,对方也一样；而全双工位是两者之间都能发送和接受数据，并可同时发送和接受。像互联网就是典型的例子。
信息输送的过程也有同步和异步之分：同步的意义在于发送数据时数据线和时钟线是同步的，也就是数据信号和时钟信号同时由CPU进行发送，这需要彼此都要专门的时钟信号来进行传送和接送，并且是强制性的，这种方法的特点在于它的速度极快、但相应占用CPU的工作时间也相对的要长、同时技术难度也非常的大。它的要求在于在一帧的数据传送中不能有一位的误差，不然的话整个数据将发生错误，这在硬件上是一个比较大的难度。在一些专用的设备中应用的越来越广泛，像专用的医疗设备、数字信号设备等，在比较单一数据的传输中，它的效果非常的好。
而异步是应用范围最广泛的，这得益于它的技术难度相对要小、同时不需要配制专门的时钟信号、它的特点在于，它的数据是间隔性的，离散性的发送和接受，当CPU太忙的时候可以停顿性去工作，在硬件上也减少了难度，同时数据的丢失相对要少，我们可以通过数据的检测来观察我们发送的数据是否有错误，像奇偶法、累加法和八位效验法等，都可以用来帮助我们检测发送的数据是否有错误发生，通过反馈来进行辨别。
信息的传送口线有串口和并口之分：通常的PLC是8位机，当然也有16位机。我们在发送数据的时候可以是一位一位的发送给对方，也可以8位8位的将数据发送到对方，一位和8位区别也就是我们所说的串口发送数据和并口发送数据。串口速度比较慢，但只要两条或者三条口线就能解决问题，并能借用电话线来进行远程控制。而并口的传送速度是极快的，它是串口的256倍，在
短距离占有优势，由于是TTL电平，一般限于1米的范围，它并不适用于长距离的数据传送，这样成本太昂贵了。
很多的情况下我们总喜欢采用串并转换芯片来进行传输，这种情况下不需要我们进行过于复杂的寄存器设置了，而直接通过数据传送指令进行数据交流，但在通信中并不是一个十分可行的办法，因为在发送数据的时候对方的PLC必须一直等待你的数据输出，它不能去做其他的工作。
当你在看书的时候，你听到有人敲门、你停下手上的事情、去打开门、并同敲门者对话、这个时候电话响了、你示意接个电话、在接完电话后、回过头来同敲门者继续对话、对话完毕后、你再继续看你的书，这种情况我们把它称为中断，它具有权威性，也具有优先性，PLC具备了这样的功能。它的特点在于我们在设备的操作过程中可能会遇到紧急的突发事件，我们要立刻的停下手上的工作，去处理更重要的事情，这种情况是我们经常所遇到的，PLC在去执行紧急的任务时，总会先保存目前的状态，比如程序的地址，CPU的累加器数据等，就像我们去开门时要记下我们看的书在第几页了或者干脆作个记号，因为我们待会还要继续接着看后面的书。CPU总是按照我们的意愿去做应该做的事情，但你错误的给它一件事情，它也会同样的去做，这一点我们必须注意。
中断并不是只有一个，有时会同时存在几个中断，中断具有优先的级别，他们会根据人的要求去执行更高级别的中断。这种中断中的中断也就形成了中断嵌套。当然中断的级别根据各种PLC内部CPU的资源有关，同时也跟堆栈的容量大小也有关系。
中断的内容有很多种，比如外部中断、通信中的发送和接受中断、定时和计数的时钟中断、还有WDT复位中断等，它们丰富了CPU在处理各种事务时响应种类。这样讲也许你并不能完全理解中断的内部结构和操作顺序，我们做一个小小的例子来说明.
每一个设备总是不会忘记有一个按钮，它也是在我们遇到紧急情况时使用的，那就是急停按钮。当我们遇到人身事故和意外情况时我们只要按下它，机器立即停止所有的操作，并等待处理完意外后再恢复操作。急停按钮连接PLC 内部CPU的内部IO接口上，当按钮给CPU一个外部触发信号时，CPU对IO进行再次检测，当确认有外部触发信号时，CPU保护现场并将程序计数器自动转到相
应的外部IO中断程序中去，当外部中断程序处理完毕，程序计数器返回到主程序继续工作。有一点可以说明的是我们一般会把急停按钮的外部中断升至最高级别，从而保证安全。
当我们在工作完一个工件时，给PLC一个信号，将PLC的内部计数器加1来计算我们一天的工作量时，一个简单的计数器能解决问题，当然它们也能够在掉电的情况下保持数据，促使数据不丢失，这也是我们所渴望的。
PLC还具有高级计数器的功能，当我们在接受一些高速的数据时，这里所说的高速是在在微秒级的数据，比如条码扫描机在不断的扫描数据，数据处理器DSP计算的高速信号等，我们就要采用到高级计数器来帮助我们进行计数。它在PLC执行程序时一旦发现高级计数器对应的中断，就会立即放下手上的工作。经过再次编程的梯形图程序说明我们在执行程序时高级计数器会自动的执行对应的工作，从而将高级计数器的级别升至高一级别。
你也许听过太多的这个词:“死机”，大致的意思是CPU工作量过大，内部资源不足等情况造成程序无法运行。PLC也有类似的情况，在PLC内部有一个看门狗WDT，我们可以设置WDT一个程序运行的时间，当程序运行过程中出现程序跳转错误时或者程序繁忙时，程序的运行时间超过WDT的设置时间，CPU转而WDT复位状态。程序重新开始运行，但对中断不会进行破坏。
PLC的发展已经从单一的模式进入了通信的网络时代，并同其它的工控网板和IO卡板轻易的进行共享。组态软件可以将所有的这些硬件连接起来，通过更直观的动画图片来进行控制，并可以通过互联网在异地进行控制，像神舟五号的发射就是采用这种办法来使飞船升空。
更高层次的发展需要我们不断的努力来取得。PLC的出现已经足足影响了几代人，我们也从上一辈的经验中获取了更多的知识和教训，来不断的发展PLC 技术，将它推向更高浪潮。
了解可用的PLC网络的最佳选择，其应用将确保有效率和灵活的控制系统设计。可编程逻辑控制器（PLC的）能够支持多种通信方法的范围，使之成为一个理想的控制和工业自动化和控制应用各种设施数据采集装置。然而，有一些混乱，因为这么多的可能性存在。为了帮助消除这种混乱，让我们的通讯名单，可什么时候他们会是最好的应用。
为了了解PLC的通信多功能性，让我们首先定义描述的各种制度的用语：ASCII码：这代表着信息交换。1，当字母“A”是传播，例如，它会自动编码为“65由发送设备”。接收设备转换的“65”回答。因此，不同的设备可以相互通信既是使用ASCII代码的其他长。
ASCII的模块：这个智能PLC模块是用于连接到PLC的通信也使用ASCII码作为车辆等设备的能力。
总线拓扑结构：这是一个线性局部区域网络（LAN）的安排。 A条，其中个别节点成为窃听通讯电缆主要在单点和广播消息。这些消息对旅游的连接点从两个方向的巴士，直到它们被消耗在每个终端的巴士底。
CPU：这代表“中央处理单元”，这其实就是一台计算机，可编程控制器，智能设备或其他地方的算术和逻辑运算的执行和指令被解码和执行的一部分。
菊花链：这是对单个设备中的PLC网络，连接描述在那里，每个设备连接到下一个和通信信号从一个单位传递到下一个顺序的方式。
分布式控制：这是一个自动化的概念，即一个自动化系统的部分是由单独的控制器，这是在位于其附近地区的直接控制（控制分散控制系统及遍布出）。
主机电脑：这是一个被用来转移的PLC 计算机网络的数据，或接收从一个PLC数据的计算机。
智能设备：这个术语描述了自己的CPU配备任何设备。
I O：这代表“输入和输出”，这些模块处理数据到PLC（输入），或从PLC （输出信号）至外部设备。
Kbps：这代表“千比特每秒”，这是一个衡量的电子数据传输速率。
Mbps：这第一个字母。“百万比特每秒”
节点：本术语适用于任何立场或在网络电台之一。每个节点包含一个装置，可以与网络上的所有其他设备。
议定书：数据的定义是怎样安排的编码和传输网络上。
环形拓扑结构：这是一个局域网的安排，其中每个节点连接到两个其他节点，在一个连续的，封闭的，圆形的路径或导致邮件循环流通，通常在一个方向。有些环拓扑结构有一个特殊的“环回”功能，让它们继续发挥作用，即使主缆斩断。
RS232：这是描述具体的线路连接，电压等级的串行通信IEEE标准，和其他经营通信电子数据参数。此外，还有其他一些遥感的标准。
串行：这是一个电子数据传输计划，信息传输一次一个位。
串行端口：这通讯上，它被设置为串行通讯设备接入点了。
星型拓扑结构：这是一个局域网的安排方式，节点连接到彼此通过一个中央枢纽，它可以主动或被动。活跃的中心执行诸如路由和维护信息网络的职责。中央枢纽只是一个被动的传递沿线的所有连接到它的节点的信息。
拓扑：这涉及到一个节点的具体安排在彼此的关系网络。
透明：这个术语描述事件或过程的自动成一个系统，不需要特殊的编程或操作员提示兴建。
现在，我们正在与这些条款熟悉，让我们看看它们是如何在现有的描述PLC 网络选项。
PLC网络方案
PLC的网络提供一个网络方案，以满足特定的控制和通信需求的各种你。典型的方案包括远程I O，同辈对同辈，和主机通信，以及局域网。这些网络可以提供可靠和成本之间的有效沟通少两个或几个100的PLC，计算机很多，和其他智能设备。
许多PLC的厂商提供的专用网络系统，是独一无二的，不会与另一作出的PLC。这是因为不同的通信协议，命令序列，错误检查计划，并通过传播媒介每个制造商使用。
但是，它有可能使不同的PLC的“交谈”彼此;什么是需要的，是为连接（第ASCII码接口），以及与软件的大量工作。
远程I 0系统
一个远程I O配置，如图所示。4A条，已实际投入一些从控制器和CPU的距离和产出。这种类型的系统，它可以作为一个“主人和奴隶式”的配置描述，使许多遥远的数字和模拟点，由一个单一的PLC控制。通常情况下，远程I O 的连接到CPU通过双绞线或光纤电缆。
远程I O配置可以极具成本效益的控制，是只有少数的I O点是在分离领域需要广泛的解决方案。在这种情况下，它并不总是必要的，或与此有关的
实际，在每个站点有一个控制器。它也不是不切实际的个别硬线交回给长途跋涉的CPU每个I O点。例如，远程I O系统可用于购置设备或设施从远程位置的数据。信息，如周期时间，计数，持续时间或事件等则可以被送回PLC的维护和管理报告。
在远程I O配置，主控制器民调苦练的I 目前我的O O状态。远程I O 系统响应，然后与主PLC的信号，远程I O来改变输出状态，由在PLC的内存控制程序决定。这整个周期出现每秒数百次。
对等点对点网络
同行的对等网络，如图所示。4B条，加强协调控制分散在不牺牲可靠性的控制功能。在这种类型的网络，众多的PLC连接到彼此在一个菊花链的方式，和共同的记忆表中的每个内存复制。这样，当任何PLC的数据写入到这个内存区，该信息会自动转移到网络中的所有其他的PLC。然后，他们可以使用他们自己的经营方案此信息。
同侪对同侪网络，每个网络中的PLC是为自己负责控制现场，只需要为它自己的责任领域编程。这大大降低了网络方面的编程和调试的复杂性;因为所有通信发生对用户透明，通讯编程是减少到简单的读取和写入报表。
在点对点的对等系统，有没有主人的PLC。但是，它可能指定作为掌握PLC 的一组作为一个控制器类型使用。这可用于PLC的然后接受来自运营商输入端子输入信息，例如，把所有必要的参数到其它PLC和协调各种活动测序。
主机电脑联系
也可连接的PLC与计算机或其他智能设备。事实上，大多数的PLC从小到非常大的，可直接连接到电脑或下降一个多主机通过RS232C或RS422端口的计算机网络的一部分。这种电脑组合，最大限度的控制功能的PLC控制和数据采集，以及计算机，数据处理，文件和操作界面。
在一个PLC 计算机网络，所有通信都是由主机电脑，它是连接在一个菊花链方式对所有的PLC。这台计算机的网络地址单独的PLC和每一个具体的信息要求。该处理的PLC然后发送该信息的存储和进一步分析的计算机。这个周期发生每秒数百次。
主机电脑也可以帮助编程的PLC;强大的编程和文档软件方案可供开发。然
后程序可以写在接力阶梯逻辑的PLC电脑并下载。这样，你可以创建，修改，调试，并通过计算机终端显示器PLC程序。
除了主机，PLC的接口往往必须与其他设备，如大型建筑物的安全和管理系统操作界面终端。虽然很多智能设备可以通过传统的RS232C通信端口和串行ASCII码的PLC直接，一些没有能力的软件接口与个人的PLC型号。相反，它们通常在固定的传送和接收的数据格式。它的PLC程序员有责任提供必要的软件接口。
最简单的方法来提供这种接口的固定格式的智能设备是使用PLC的一个ASCII 基本模块。这个模块基本上是一个小型计算机插入PLC的巴士。配有RS232端口和基本程序，该模块可以很容易处理与周边设备的ASCII通讯，数据采集功能，编程序列，“数字运算，”报告生成和显示，和其他要求。
访问，协议和调制功能的局域网
通过使用标准的接口和协议，允许局域网的设备组合（可编程控制器，个人电脑，电脑主机，操作界面终端等），从许多不同的供应商进行通信与网络上的其他人。
访问：局域网的接入方法可防止在网络上的时间超过一个消息的发生。有两种常见的访问方法。
碰撞检测是其中的节点“听”到网络和传输只有当网络上有没有其他消息。如果两个节点同时传输，碰撞检测和两个节点转发，直到他们的消息通过正常。
令牌传递允许每个节点传送只有当它在一个特殊的电子称为令牌信息占有的。令牌传递从节点到节点，使每个有机会传送不受干扰。令牌通常有一个时间限制，以防止绑了很长时间的道理一个节点。
议定书：网络协议的方式界定和安排的信息在局域网上传输编码。下面是两种常见的类型。
专有的协议是唯一的消息的安排，并由他们与该供应商的产品只能使用特定的供应商开发的编码。
开放的协议是根据行业标准，如TCP IP协议或ISO OSI的模型，并公开发表。
调制：调制是指网络邮件的方式传输编码的电缆进行测试。两种最常见的类型是宽带和基带。
网络传输接口
PLC的通信绝大部分都是通过RS232C及双绞线电缆。大多数的PLC有一个RS232端口，并处理与东道国电脑，打印机，终端通信能力，以及其他设备。最大传输速度为19.2 Kbps。
距离和数据传输率是各种接口标准。他们的实际表现是传动装置制造商之间的功能和显着变化。因此，你应该征询实际距离和数据传输速率能力的制造商的规格唯一的限制是真正的RS232C 50英尺的距离设备之间的建议。虽然RS232C装置往往可以达到比这更大的布线距离的“不平衡”在更大的敏感性结果的界面设计，周围的电噪音和降低数据完整性。尤其是这样的地方电磁干扰（EMI）和射频干扰（RFI）是已知的存在。
当传输距离更长，还需要的RS422是一个更好的选择。不同的是RS232C接口，RS422接口，是“平衡”。其主要方面包括各信号的信号地面两条电线是在相反的逻辑电平始终。因此，该接口可以实现更长的传输距离（4000英尺）和更高的数据（90 Kbps）的传输速率。运行在较短（少于50英尺），数据传输可以达到10 Mbps的。
光纤通信正在赢得更多人的接受，并正在越来越多的设备使用。光纤电缆是几乎不受恶劣的环境条件和电气噪声。此外，这些链接可以跨越很长的距离和传输数据非常高的速度。例如，在一些局域网系统中，这些链接可以在相对高的传输速度和范围之前，需要一个中继距离长。当中继器的使用，几乎无限的距离可以达到。