Read/Write tags from Control to Compact logix

[Conor 4]

Hi guys, I was wondering if someone could tell me the best way to do this. I have a Control Logix L5555. It has a few cards on it. One of the cards is an Ethernet 1756-ENBT/A. Connected to this is an L35E. I am looking to read most of the tags into the Control Logix, but was wondering what was the best way to do this. I have set-up a MSG instruction and am able to read values this way. I have only read one REAL tag to test my comms. I would be looking to read DINT's and BOOL's and REAL's. I would say I need to read about 50 tags. If I was to use the Message instruction then I would have to write a lot of messages and I would also need to stagger them as not to overload the PLC (correct me if I am wrong) Hopefully someone can help me Thanks, Conor

[Mozelstein 0]

You can move everything you want to read into an array then just do one message. Or a couple of arrays if you want to keep like data together. I'm not super familiar w/ the L35E but another option might be to do produce/consumed tags.

[Conor 4]

Thanks for your quick response. I will have to read up on the produced/consumed tags

[BobLfoot 302]

Produced/Consumed Tags will be the most elegant way to move data if both CPU support them. As a fallback if Produced/Consumed is not an option or you need to patch something into a set of CPU you can't take to program mode then the message instruction is your cup of tea. Most people use Reads and Writes without taking time to asses what makes the most sense. I prefer to Use Reads whenever possible for a number of reasons. 1 - The Read is 2x to 4x faster than a Write for the same amount of data. 2- Reads document well in the PLC receiving the data, while Writes do not. Also make sure you write programming/code to hand the "my communications are hosed" case. Nothing worse than a pump thinking the tank is empty when it's overflowing because the message passing level data is faulted.

[NatiJacket 0]

I second (third?) the recommendation for produce/consume. You might also want to take a look at User-defined Data Types (UDTs). This would let you combine much of your data into a single tag, minimizing your connections and/or MSG instructions. This will also help you since only DINTs, REALS, or UDTs can be produced/consumed. You just have to make sure that the UDT is added to both the Control and Compact logix controllers. Here are some manuals that might help Produce/Consume in Logix 5000: http://literature.rockwellautomation.com/idc/groups/literature/documents/pm/1756-pm011_-en-p.pdf Programming guide (w/ UDTs starting at page 38) http://literature.rockwellautomation.com/idc/groups/literature/documents/pm/1756-pm004_-en-p.pdf

[Conor 4]

Hi guys, Sorry for not getting back earlier, but I was very busy and am only getting back to this now. I read through the link that NatiJacket included (thanks), and I tried to setup a produced tag, but of course everything was greyed out. I went off line and was able to modify the "Type" of the tag. If I change all of my tags that I need to Produced, do I need to download to the controller?

[Conor 4]

Hi guys, As I have the tags set-up in the PLC in which I need to change to produced, instead of me changing this off-line and downloading, would it be easier for me to set up alias tags that are produced. I have memory space in the PLC. Ok, scrap that. I just checked and Alias is one of the options that produced is in Edited 29 May 2012 by Conor

[Conor 4]

Hi guys, I was able to wrangle some downtime to be able to download the programs to my PLC's. I set up one UDT produced/consumed in both PLC's to test connections, and it works fine. I was wondering about the RPI setting for the consumed tag. The consumed tag is in the Control Logix (1756-L55), running V16.21. The produced tag is in the Compact Logix (1769-L32E). I set the RPI of the tag that I tested to 4 ms. I needed to change 24 tags to produced and create the same amount of consumed in my L55. Is it alright to leave the RPI set at 4 ms in all of these tags? Another question. I have about 4 BOOL tags that I need to read. What is the best way of reading them? Thanks, Conor