glenncooper
Member
Hello. I've reviewed the available posts regarding messaging with the 5/05, but still find myself short of a workable solution. Our network is a bit tricky, but I'll try to explain. We have 5 production lines that have three PLCs each (2 SLC5/05s and a Micrologix with the Ethernet adapter). The network structure makes each of these production lines completely isolated from the others. I've opted to use the most under-utilized SLC to handle the MSG statements. The communications between processors on a given machine are rock solid, and work fine. This is true despite the fact that I'm not using any logic to try and coordinate the MSG instruction's execution. Each MSG instruction is always true, and the "read error" and "read done" bits unlatch the "Read Enable" bit. This strategy is apparently based on some very old A.B. reference, as was indicated in an earlier post.
The situation then gets tricky. We have another single SLC5/05 that communicates with all five of these production lines. We're using a level 3 switch, and have no problem establishing communications between this common SLC and the five production lines, while simultaneously keeping the five lines isolated from each other. I feel pretty solid about the network architecture for these. (FYI - all of the SLCs use an addressing structure like: 10.10.x.yy, where x is 1-5 for the production lines and 7 for the common PLC, and yy varies for the processors within a given machine. With the correct subnet structure and the use of the level 3 switch we don't appear to have any issues establishing communications between processors).
But I'm having tons of problems trying to get reliable messaging between this common SLC and the five lines. I've tried having the MSG statements in the common SLC, which gives me 10 MSG instructions. I haven't tried anything to coordinate the triggering of these, however. This hasn't worked well at all.
And I've tried putting the MSG instructions in the production line PLCs and have them each point to this common PLC. This also hasn't worked well. The fact that neither scheme has worked is no surprise given that there are 10 MSG instructions with no coordination about when they are enabled.
I've seen a couple of posts in this forum about using the DN and ERR bits of one MSG instruction to trigger the next MSG instruction, which gives you the fastest MSG execution time without having these MSGs pile on top of each other. This conceptually seems nice, but I have big concerns about what happens if one of the MSG instructions is returning an error - seems like this will trash the entire scheme.
So the sequential triggering of the MSG instructions seems like the way to go. For the communications between this single PLC and the five lines, I'd like to move the MSG instructions back to the single SLC, but I need a reliable way to sequentially trigger them without bringing the whole system to a crawl if one of the MSGs is in error.
Should mention: This common SLC is a 1747-L552 Series C FRN3-9, which indicates that it can support 64 connections on channel 1 (but is running between 6 and 7).
Sorry for the long post - any help resolving this would be FANTASTIC!!! Thanks!
The situation then gets tricky. We have another single SLC5/05 that communicates with all five of these production lines. We're using a level 3 switch, and have no problem establishing communications between this common SLC and the five production lines, while simultaneously keeping the five lines isolated from each other. I feel pretty solid about the network architecture for these. (FYI - all of the SLCs use an addressing structure like: 10.10.x.yy, where x is 1-5 for the production lines and 7 for the common PLC, and yy varies for the processors within a given machine. With the correct subnet structure and the use of the level 3 switch we don't appear to have any issues establishing communications between processors).
But I'm having tons of problems trying to get reliable messaging between this common SLC and the five lines. I've tried having the MSG statements in the common SLC, which gives me 10 MSG instructions. I haven't tried anything to coordinate the triggering of these, however. This hasn't worked well at all.
And I've tried putting the MSG instructions in the production line PLCs and have them each point to this common PLC. This also hasn't worked well. The fact that neither scheme has worked is no surprise given that there are 10 MSG instructions with no coordination about when they are enabled.
I've seen a couple of posts in this forum about using the DN and ERR bits of one MSG instruction to trigger the next MSG instruction, which gives you the fastest MSG execution time without having these MSGs pile on top of each other. This conceptually seems nice, but I have big concerns about what happens if one of the MSG instructions is returning an error - seems like this will trash the entire scheme.
So the sequential triggering of the MSG instructions seems like the way to go. For the communications between this single PLC and the five lines, I'd like to move the MSG instructions back to the single SLC, but I need a reliable way to sequentially trigger them without bringing the whole system to a crawl if one of the MSGs is in error.
Should mention: This common SLC is a 1747-L552 Series C FRN3-9, which indicates that it can support 64 connections on channel 1 (but is running between 6 and 7).
Sorry for the long post - any help resolving this would be FANTASTIC!!! Thanks!
