Sign in to follow this  
Followers 0
plcnovice

Slc 5/04 Communication

7 posts in this topic

Hi There Well i have got a very tight deadline on this project, and the surprising thing is i didnt even write the existing code. Before i tell you the problem, let me explain you a little background: we have a SLC5/04 working at the site and it is communicating over DH+ network. Now the problem is as follows: The client want us to read from and write to this plc through a site plc which is another SLC over DH+ network. He has given us a list of data file addresses (some of them are R/W or some of them are only write or read), which he wants to us to make them available on DH+ network. In other words, he is looking for a integer data file or files that he can message back and forth to and from the site PLC so that he can read the information and write to them as well. The datafile adddresses are in bit and integer formats. Like i have already introduced myself on this forum a novice programmer, so i really have no clue how to do it, if anyone of you can help me out in this regard, it will make my life so easy. Thanks in advance. PLCnovice

Share this post


Link to post
Share on other sites
I would suggest you start off by downloading the SLC instruction set Reference Manual. Get it here: http://literature.rockwellautomation.com/i...rm001_-en-p.pdf Chapet 12 covers communication instructions, and has ladder logic examples. Post back if you have specific questions.

Share this post


Link to post
Share on other sites
Thanks Ken Moore for your kind advice. First of all, the client wants a integer data file or files in our plc so that they msg back and forth to and from the site plc. So in this context how would i implement it. do i have to create a data file containing all the addresses which he is interested in reading and writing from a site plc? if yes, then how can i implement it..... I guess my job is just to make the data available at DH+ network.... Regards

Share this post


Link to post
Share on other sites
If you look at the MSG instruction, you will see that you can read any floating, bit or integer file, starting at any address. However there is a limit on the size of any one MSG. So....to answer your question it depends. If the data you need to read/write is somewhat conslolidated, ie all the data is in one N file or one B file, just use a couple of MSG instructions for each location. But... If you need two words from N7 and one word from N11, and three words from N33 etc.... It would make sense to "map" the required words to and from a "message" file. Basically in your plc you will have to use moves and or copy instructions to get all your data in one file, then if this data is being written to from a remote PLC, you will also have to move it from your message file to the "field" locations, or edit your program to just use the remotely written addresses. Like I mentioned earlier, it all depends. There is no one size fits all answer. You don't have to have a "message" data file, it's just more effiecent to have one or two MSG's than 7 or 8, it may not be an issue now, but somewhere down the line, network traffic might become an issue, I always try to keep my message traffic as effecient as possible, who knows what the future may hold. Since you're new, I would start off by passing one dummy word back and forth, that way you can work all the kinks out of the message instructions. Then once you get the hang of it, expand your MSG instructions to cover what really needs to be done. Hope this helps.

Share this post


Link to post
Share on other sites
Hi Moore Thanks a lot for your efficient advice and guidance. Yeah that makes more sense that if i make a msg file in my plc. In this way i have a few questions regarding msg file: 1) can i make one data file that contains all bits, integers, floating points etc? or a msg file has a special structure? 2)what really you mean by map the required words? 3) by saying coping or mov instruction, you mean to say a particular address that is required shd be moving into the msg file? really dont understand this Thanks very much in advance

Share this post


Link to post
Share on other sites
I hate to be harsh, but have you read any of the suggested reading material posted here and at plcs.net? I think that if you read the documentation, it will answer a lot of your questions. If you read the material and still cannot get a handle on the situation, perhaps you should hire a local professional to assit you.

Share this post


Link to post
Share on other sites
Ok, i guess after taking a look at the rockwell knowledge base examples for SLC communication, i think our plc is acting like a slave, just giving what the site plc (Master) is asking? So in this case i dont think i need any msg instructions or stuff, all i need is to make a data file, place all the required data addresses in it and maps the read and write values back to the main program. Now the problem is i have a lot of data addresses of type bits, inetgers, etc how can i gather them under one msg data file and how can i map these values back to the main program? any help would be appreciated in this regard

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now
Sign in to follow this  
Followers 0