ML1100 modbus

[avkiv14]

Hi all.
I have some problems with ML1100 and modbus rtu, I have 2 nodes
with solcon HRVs soft starter and MPS3000, ML has 1763-NC01,
the ladder has 8 MSG to read data, the net works good for one day or two, then stop. I power off the ML and power on and MSG begin to work again.
I don´t Know what to do...

Could someone help?
thanks.

 

[bernie_carlton]

Post your program (zip it first)

 

[dmargineau]

Are the MSGs "cascaded" or they trigger independently of each other?

 

[avkiv14]

program´s same as answer ID 33774.

Hope you can see the file.

 

[rguimond]

I'd recommend the following:

1. On the first rung, don't enable MG9:0 if MG9:0 isn't enabled. Instead, trigger it if first-pass bit is set OR if MG9:6 in DN or ER. I'd say MG9:0 runs virtually all the time
2. I always add a third OR befor each MG instruction - MG9:x/TO. This will enable the next message if the previous one times out.

 

[zhoudq]

post you program error code and error discription

 

[avkiv14]

post you program error code and error discription

error code 37
message timed out in local processor

 

[Ken Roach]

If you were to put a protocol analyzer on the wire and run that program, the messages you would see on the network (named by their Control Element) would be:

MG9:0
MG11:0
MG9:1
MG11:1
MG9:0
MG11:0
MG9:2
MG11:2
MG9:0
MG11:0
MG9:3
MG11:3

The first message in each subroutine is alternating with one of the other messages in the "sequence".

The logic in RA Knowledgebase document 33774 is actually intended to work that way: it writes the Command word to the drive frequently, and then reads the status information less frequently. That logic is also intended as a "quick start" and doesn't consider the consequences of serial data errors.

(continued)

 

[Ken Roach]

I prefer to write logic that triggers MSG instructions periodically and sequentially.

In addition, you are using MSG instructions inefficiently; most of your MSG instructions read only one Modbus element each, and many of them are adjacent.

For example,
MG11:0 reads Modbus address 40257, Length 1, into MicroLogix N21:0
MG11:1 reads Modbus address 40258, Length 1, into MicroLogix N21:1

You could combine both of those messages into a single Message that reads Modbus data starting at 40257, Length 2.

In fact, if you were willing to change where your data is stored in the MicroLogix 1100, you could read the whole data range in the MPS3000 routine in one or two MSG instructions by reading a larger block of data.

(continued)

 

[Ken Roach]

Bernie is probably the most experienced Forum member on MicroLogix Modbus messaging, since he has built bulletproof logic for drive control, and he might be able to provide some additional advice.

Modbus is by its nature a one-message-at-a-time protocol, and I think that Rockwell implemented a one-message-at-a-time handler for Modbus messages in the MicroLogix.

So you want your logic to trigger one message only, then wait for that message to be complete (/DN or /ER), then trigger the next message. Your existing logic triggers 2 messages every sequence cycle, then 2 messages (the MGxx:0 elements) on the next PLC scan.

I've decided against posting an actual screenshot or program, because I don't have the equipment to fully test this logic.

 

[avkiv14]

Bernie is probably the most experienced Forum member on MicroLogix Modbus messaging, since he has built bulletproof logic for drive control, and he might be able to provide some additional advice.

Modbus is by its nature a one-message-at-a-time protocol, and I think that Rockwell implemented a one-message-at-a-time handler for Modbus messages in the MicroLogix.

So you want your logic to trigger one message only, then wait for that message to be complete (/DN or /ER), then trigger the next message. Your existing logic triggers 2 messages every sequence cycle, then 2 messages (the MGxx:0 elements) on the next PLC scan.

I've decided against posting an actual screenshot or program, because I don't have the equipment to fully test this logic.

Thanks for taking time to answer, Ken
I´m going to make change in the program, then I let you Know.

 

[bernie_carlton]

I think I've posted these before but just in case ...

This shows our method for implementing round-robin communication with 4 Powerflex drives. It's on a Micrologix 1100 so the free software opens it. A PDF is included for those without the software.

I'm not saying this is the only or best way, it just works for us.

 

[avkiv14]

I think I've posted these before but just in case ...

This shows our method for implementing round-robin communication with 4 Powerflex drives. It's on a Micrologix 1100 so the free software opens it. A PDF is included for those without the software.

I'm not saying this is the only or best way, it just works for us.

It works for us too.
Once I made these changes, all MSG´s began to work.
Now, I have the information without any problem.

thanks for your help Bernie.
here is better than take RA training.

 

[avkiv14]

thanks all of you, for the answers