U_251915f6-0eb6-49a4-be25-0094116af448

When I use more than 10 MB_MASTER commands, MB_MASTER commands with addresses 8-9-10 switch to 16#8070 failure. I can receive data from 7 other devices properly. When I delete MB_MASTER with address 11, the error goes away. And I can get data from 10 MB_MASTERs properly. What is the reason of this? I know that I can connect up to 32 devices with RS485. but I can't connect more than 10 pcs.

Guess: Overlapped calls or overlap memory or too big FB.
Difficult to answer without seeing your code.

As far as I can tell 16#8070 = "All internal instance memories are in use".
What is the size of your FB and the instance DB that connects to it?
Is the optimized setting on or off for this managing FB?

Hello, 

Plc Load Memory 9% Used, Work Memory 30% Used. 

I don't think there is any problem. My module, cm1241 rs422/485, I could not find the cause of the problem when I connected more than 10. Attached is the pdf of the program.

There are 2 things that needs changing.

1) Do not trigger the MB_MASTER on a timer. Have the DONE / ERROR state of the MB_MASTER tell you when the next instrument should be queried.

2) Do not use multiple MB_COMM_LOAD. This is probably the cause of your problem.

This would mean that the design concept changes. Have one MB_COMM_LOAD and one MB_MASTER. Have the parameters to MB_MASTER change according to which slave needs attention. The tricky part is that MB_MASTER.REQ needs to see a OFF -> ON transition to function.

There is a very old sample project that uses LAD which you might find helpful. That is attached to this message. Focus on the structure of the Modbus instructions' usage.