【正文】 r bee the topic that we fail, but stay to our is a concern to e 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 prehended 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 prehend more and easily, in a lot of equipments, the people have already no longer hoped to see too many control buttons, they damage not only and easily and produce the artificial error easiest, small is not a main error perhaps you can still accept。 A work of half is also 2 and can send out similar to accept the data, but can39。s (PLC39。s see how they are used in describing the available PLC work options. PLC work options PLC works provide you with a variety of working options to meet specific control and munications requirements. Typical options include remote I/O, peertopeer, and host puter munications, as well as LANs. These works can provide reliable and costeffective munications between as few as two or as many as several hundred PLCs, puters, and other intelligent devices. Many PLC vendors offer proprietary working systems that are unique and will not municate with another make of PLC. This is because of the different munications protocols, mand sequences, errorchecking schemes, and munications media used by each manufacturer. However, it is possible to make different PLCs talk to one another。 powerful programming and documentation software is available for program development. Programs then can be written on the puter in relay ladder logic and downloaded into the PLC. In this way, you can create, modify, debug, and monitor PLC programs via a puter terminal. In addition to host puters, PLCs often must interface with other devices, such as operator interface terminals for large security and building management systems. Although many intelligent devices can municate directly with PLCs via conventional RS232C ports and serial ASCII code, some don39。s product only. Open protocols are based on industry standards such as TCP/IP or ISO/OSI models and are openly published. Modulation: Network modulation refers to the way messages are encoded for transmission over a cable. The two most mon types are broadband and baseband. Network transmission interfaces The vast majority of PLC munications is done via RS232C and twisted pair cables. Most PLCs have an RS232 port and are capable of handling munications with host puters, printers, terminals, and other devices. Maximum transmission speed is Kbps. The distance and data transmission rates a。s no master PLC. However, it39。s used to transfer data to, or receive data from, a PLC in a PLC/puter work. Intelligent device: This term describes any device equipped with its own CPU. I/O: This stands for inputs and outputs, which are modules that handle data to the PLC (inputs) or signals from the PLC (outputs) to an 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 work. Each node incorporates a device that can municate with all other devices on the work. Protocol: The definition of how data is arranged and coded for transmission on a work. 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 have a special loop back feature that allows them to continue functioning even if the main cable is severed. RS232. This is an IEEE standard for serial munications that describes specific wiring connections, voltage levels, and other operating parameters for electronic data munications. 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 munications access point on a device that is set up for serial munications. Star topology. This is a LAN arrangement in which, as shown in Fig. 2B, nodes are connected to one another through a central hub, which can be active or passive. An active hub performs work duties such as message routing and maintenance. A passive central hub simply passes the message along to all the nodes connected to it. Topology: This relates to a specific arrangement of nodes in 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 we39。t prehend the internal structure and operation orders of the interruption pletely also, we do a very small example to explain. Each equipment always will not fet 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 have the exterior to trigge