Rslogix 500 Project

[plcnovice 0]

Hi All I am totally new to RSLogix 500 programming enviornment. And i am pretty confused with all the terminology it is using to create and manage a project. I was just wondering is there any good tutorial on RSLogix 500 that will guide me step by step procedure of the project in more general sense. To be more specific, i am not quite confidant with the data files and data table databases. For example, output data file and the input data files, according to my understanding, output file should have output modules configuration and input files should have input module configuration. But i am looking on a project, and it confused me totally, its input file has the information for input modules as well as output modules and so as output file. So right now i dont know whats going on in that project. If some one can elaborate to me the the RSLogix 500 project may be if you guys have some example project it will be a great favor to me. Thanks in advance PLCNovice

[Ken Moore 23]

Many of the SLC analog I/O modules have both input and output memory. In the case of an analog module the output memory is used to configure the module. It helps a lot to download the manual for the specific module your're dealing with. If you go to the FAQ section of this board, there are links to everything you need to get you started. http://forums.mrplc.com/index.php?showtopic=6401

[Guest]

Greetings plcnovice ... besides Ken's excellent advice, here's another idea ... if your program isn't secret or proprietary information, you might consider posting your .RSS file on the forum ... that way we can give you specific information about anything that's causing confusion ... you might want to ask your boss about whether posting the file is a good idea or not BEFORE you do it ... we'll understand if you can't post it, but it sure makes things a lot easier to explain if we know EXACTLY what we're up against ...

[plcnovice 0]

Hi Ron Beaufort Thanks a lot for you reply. The thing is my question is more generic. Like i want to know inside out about RSlogix 500 so that i can understand my project. Right now i dont know how the data files work, what is the purpose of data table databases and how input module and output module work? Also, once the program is downloaded and first time run, how does the plc read the inputs from the real world? is there any starting values we give in our ladder? all these kind of things. If you can make me understand all this then i believe handlin my project would be so easier for me. Once again thanks a lot. Regards PLCNovice

[TConnolly 13]

PLCnovice... I dont have time to address all of your questions right now, but I'll take a second and give a brif overview that I hope helps.. In the SLC500 family of PLCs the input and output data files are a copy of the real world input/output information from the IO cards. Right at the beginning of a scan the processor takes a snapshot of all the data in the IO cards and places that snapshot in the input image table, or the I file. As the processor scans the program it will write changes to the output image file, or the O file. Actual changes are not made to the physical outputs yet, only to the output image file. After the PLC completes the program scan it will then copy the output image file, the O file, to the physical IO cards. Then the program will take a few microseconds to do some housekeeping and communication port activities, then it will repeat the operation. The input and output image files will be set up by RSLogix500 according to the IO configuration specified under Project->Controller->IO Configuration in the project tree on the left hand side of your screen. The input and output addresses that you see in the I and O files are a reflection of what kind of cards are configured there. If you have a fixed IO PLC such as a fixed SLC500 or a Micrologix, then you will have at least one I:0.0 and O:0.0 word for the base unit IO. The base unit is considered slot 0. If you have a fixed unit with more than 16 inputs or outputs, you will see more than one word for slot 0, as in I:0.0 and I:0.1. If you do not understand the addressing scheme, take a moment and review it in SLC500 help or in the Instruction Set Reference Manual which you can dowload from the AB website literature library at www.ab.com. Be advised for future reference, If you are using RSLogix5 or Logix5000 there are some differences in how IO is configured and scanned - but lets stick to 500 for now - just note it and file it away in case you ever use one of the others. Data files are simply a section of memory you set aside for a specific purpose. To make it easy on the programmer, RSLogix500 segregates these chunks of memory by function. Therefore a chunk of memory can be set aside for bits (B files) and another chunk can be set aside for timers (T files) and another chunk for counters (C files), integers (N files), and floating point number files (F files). Unlike some other PLCs, you are not fixed in the number if timers you can allocate for example, but rather you can allocate as many timers as you think you will need. Edited 28 Feb 2006 by Alaric

[hipoint2 0]

Very good explanation. You then break down even farther. For example if you had a digital input card in slot 2 of your rack and in the program you see I:2/0, which means in the Input image file, word 2, bit 0. Same goes for the outputs. If you had a digital output card in slot 3 of your rack then O:3/0 would mean Output image file, word 3, bit 0. Most of the other files, except the B file you USUALLY use the whole word, but it all depends on the programmer.

[plcnovice 0]

Hi Alaric Thank you very much for your beautiful explanation, it really clears me a lot of things in my mind. One more thing i would like to ask you, when you first time install the plc on an application and connect it with the field instruments like sensors and stuff, how would it read data from it. there is a possiblity that the data it is being read from the input modules is not stable. How do we check all this and how can we make a safe program depending upon this situation. Thanks a lot plcnovice

[TConnolly 13]

Well, what you are refering to is the startup process. And it will be different for every application, but every process has to have a start up state and a shut down state. It is the engineer's responsibility to make sure that such a state can be achieved. On a new project typically sections of the system will be powered up at a time with the PLC in program mode. Each of the sensors is checked to see that it is wired correctly and is feeding a signal to the PLC. Even though the program is not running input image data and output image data is read from and written to the physical IO. This allows you to observe the changes the process makes to the PLC memory without the PLC actually responding to those changes. Once you are assured that everything checks out then you place the program in run and start up the process. Sometimes I place temporary dummy permissives in sections fo the code that allow me to isolate one section of the process for debugging. I also spend a lot of time with a piece of paper and a pencil. Sometimes in this computer age we forget the usefullness of this tool.