CC-Link field bus is Japan’s Mitsubishi Electric Corporation, a main push based on the PLC system field bus, which is currently in the world field bus market, the only source from Asia, but also occupy a certain market share of the field bus. It shows a strong vitality in practical engineering, especially in the manufacturing industry has been widely used.
In the CC-Link fieldbus application process, the most important part of the system is to initialize the communication settings. At present, there are three methods of CC-Link communication initialization. In this paper, we will compare and analyze these three different initialization methods in order to find out how to choose the simplest and effective communication initialization method in different situations. This is of great practical significance for the use of CC-Link fieldbus in practical engineering, one for designers to reduce the workload and save time while ensuring design quality, and two to try to explore whether it can be further exploited and excavated CC-Link’s potential.
A brief description of the experimental system
In order to facilitate the comparison of the communication initialization method, we first in the laboratory to establish such a small CC-Link field bus system.The whole system configuration shown in Figure 1.
After the hardware connection is set correctly, you can start the communication initialization settings.
The use of three setting methods
First of all, the most basic method is used, that is, by programming to set the communication initialization parameters. The process of compiling the communication initialization procedure is shown in Fig. First, in the parameter setting section, the number of modules to be connected to the entire system, the number of retries, the number of automatic return modules and the operation specification (stop) when the CPU is paralyzed and the information of each station are written to the corresponding address in the memory. After the refresh instruction is executed, the parameters in the buffer memory are fed into the internal register area to initiate the data link. If the parameters in the buffer memory can start the data link normally, this means that the communication parameters are set correctly, then the parameters can be registered to the E2PROM via the register instruction. This is because once the parameters of the power-off internal register are not saved, and the parameters in the E2PROM even if Figure 2
The process of the communication initialization procedure
Power is still saved. At the same time communication parameters must be written to the E2PROM at one time, that is, only when initialized. After the CPU is running through the E2PROM parameters into the internal register to start the data link. It is worth noting that if the communication parameters are set incorrectly (if the parameters are not consistent with the hardware used by the system or the parameters are not consistent with the settings on the hardware), the data link will not start normally, but usually does not show where there is an error. Only by their own careful and patiently check, no other way. Conversely, if the communication parameters are set correctly and the settings on the hardware are wrong, the CC-Link communication control component provides error messages, and the diagnostic type of the error can be found by programming the diagnostic function.
The second communication setup is done using the configuration software GX-Configurator for CC-Link using the CC-Link communication configuration. The configuration software can be A series and QnA series of PLC configuration, to achieve the communication parameters set.
The whole configuration process is very simple, after selecting the master station model can be set up the main station, then add the connected slave station, and the slave settings, including the slave model and its occupied station The number of. The final configuration of the finished screen shown in Figure 3.
The basic information of each module in the configuration process will be displayed on the finished screen, the whole picture is simple and intuitive, the system configuration at a glance. However, there was a problem when the data link was started after the configuration was completed.
When “Download master parameter file” is selected, a dialog box will pop up asking you to choose whether to write the parameters to E2PROM or buffer memory. Regardless of which one of the options, the software will prompt “whether the current data link?”, If you select “Yes”, the site of the LED lights indicate normal. However, when the normal operation of the PLC reset after the re-run, the site are wrong. This shows that the configuration file does not actually write to the E2PROM, that is to say that the configuration software does not have the parameters written E2PROM this part of the function. So in this case in order to be able to use E2PROM to start the data link, it must be written in the main station “parameter register to E2PROM” this procedure, by configuration and programming to work together to start the normal data link. Obviously, this method is to use the configuration package to set the communication parameters, and then use these parameters to write these parameters to write E2PROM, this is necessary to complete the data link must be the last step. Of course, this will bring some inconvenience when used in practice, but it will, after all, omit the program that writes the communication parameters to the buffer register, and in this sense it will bring a lot of convenience to the user of CC-Link.
The last method is through the CC-Link network parameters to achieve communication parameter settings. Because this is a small Q series of PLC new features, and A series and QnA series PLC does not have this feature. Therefore, in this experiment to set the method must be used to replace the original master module Q series PLC.
The whole process is quite convenient. As long as the GPPW software in the network configuration menu, set the appropriate network parameters, remote I / O signal can be automatically refreshed to the CPU memory, but also automatically set the CC-Link remote components of the initial parameters. As shown below. If the entire CC-Link fieldbus system is composed of small Q series and 64 remote I / O modules, it is not even necessary to set the network parameters to complete the initial setup of the communication settings.
After using these three different methods, they have a more comprehensive understanding and understanding of their strengths and weaknesses.
Compile the traditional ladder sequence program to set the communication parameters of the most complex, programming time spent a long time. And in the debugging once found an error, you need a proof of proofreading, to find out where the error, so there is a lot of work. Yet it still has the advantage that other methods do not have. First of all, after editing the entire set of procedures can be very clear understanding of the entire setup process, master how the operation of the PLC, start the data link. Second, the whole idea of programming is very clear, and to prepare the correct procedures must be based on the mastery of the use of various devices on the basis of conditions, and thus in the process of the various devices can be connected to the conditions are Can have a very good understanding, and can be skilled use. For beginners and interested in mastering CC-Link communication designers are best to start here.
The biggest advantage of using the configuration software to set up is simple and intuitive, on the screen can clearly see the entire system configuration, including the number of slaves connected to the master station, the specifications and performance of each station, at a glance. And in the event of an error or to change the parameters, can be completed quickly, saving a lot of time and workload. However, it also has one of the biggest drawbacks, that is, the parameters can not be stored in the E2PROM, after reset, just write the configuration will no longer exist. If the actual application, the scene is complex, will encounter a lot of unexpected problems, if you need to reset the middle, then the configuration software will be powerless, must be re-set and then write, this will affect the work progress. Therefore, in this case using the configuration software, supplemented by the communication parameters from the buffer accumulation area written to the E2PROM program, you can complete the entire system initialization settings. In addition, the configuration software does not currently support small Q series PLC.
Finally, the use of network parameters set method is simple and effective, as long as the provisions of a certain amount of parameters to fill in the complex after the complex can be complicated procedures. In the event of an error or the need to modify the parameters, the same configuration software, can also be completed quickly, reduce the set time. However, its shortcomings, is to set the process of skipping a lot of important details, which can not really grasp the PLC’s internal operation process, more abstract. For example, after filling out a number of parameters, although the data link of the station can be implemented normally, but can not understand how these parameters are linked, how the role of how to make the data link to the normal completion of the station.
In short, the three methods are different, suitable for different purposes and different circumstances (such as different PLC series) for users to choose the flexibility. If you aim at a clear understanding of the operation of the PLC, you can use the programming method; if you want to save the designer’s workload, reduce the design of debugging time, you can use the network parameters of the method. Configuration software can be regarded as a combination of these two. In the actual application, through the network parameters to carry out the communication initialization method is one of the most superior method, convenient, reliable, full-featured three points have been very good to meet the needs of the system, shortening the CC-Link site Bus in the application of a variety of industrial applications when the design and commissioning time, reducing the difficulty of the work, more convenient for future troubleshooting and maintenance. Unfortunately, it only applies to small Q series PLC.
With the development of communication technology and control technology, I believe that in the near future fieldbus technology and its related technology will develop more mature and perfect, and will appear more convenient and powerful communication settings method, so that the future of the scene Bus technology is better applied to the scene.
Author: Department of telecommunications equipment Shanghai Jiaotong University School of Deng Ye