Modbus redundancy with COM3 of AC800M..
Is it possible to have modbus communication redundancy with COM3 of AC800M by using "Serial redundant switch"
Voted best answer
Despite not supporting Hardware redundancy it is possible to program the communication failure to disconnect the serial channel and connect to a new one.
It's possible to program redundancy Series Modbus communications with a pair of Controllers and one CI853 module. The program should switch between the Channel of CI853, and the CH3 of the Controller active, it is not need take care which controller is the active because the channel of the Controller in stand-by remains inactive.
In my experience, you must be careful that the firmware version is recent. In previous versions, the reconnection not erase the buffer communication, so channel, if it had been receiving communication frames, these would be the first to be managed by the MBRead/MBWrite with Error, and negative status (the function sent does not match with the communication frame into the buffer)
I request some more information below to understand your requirement better.
1. Are you using redundant AC 800M controllers for above Modbus redundanyc using COM3?
2. Using COM3 of one AC 800M controller, you want to switch between redundant modbus slave devices?
Please confirm any of the above.
The serial port COM3, can not be used in redundant CPU configuration
That means, when redundant CPU's are used, the only poddibility for COM (serial) port is CI853.
Integrated COM3 is not usable in this case, it can't be reached from the backup CPU.
When you use CI853, it can be single, connected to both CPU's by CEX bus (with or without BC810) In this case, each port of CI853 is reachable from Upper (active) and Lower (backup) CPU
Or you can install 2 pcs of CI853 - 1 pc for each CPU (redundancy of CI853 itself)
Its not possible to achieve modbus redundancy using inbuilt com3 ports when red controllers are used since when primary or running controller com3 port fails backup controller or sleeping controller won't take over since the program still running under primary controller only.
And more over u have to use ci853 with parallel configuration where as u can onfigure the redundancy in program level.
You can connect 2 pcs of CI853 to both CPU's like hardware redundant modules (not redundant CI853 itself like CI854 for example). Then in the software you can switch betwen COM ports from first or second modules in case of failure (2 MBConnect blocks with Channel 1 and 7, for this example). Addresses from 1 to 6 on CEX Bus belongs to upper CPU and 7 to 12 - to lower CPU on CEX bus (physical position of the module)
Redundancy for COM3 in both CPU's can't be realized in any case
This drawing is from real application?
What if CI853 is not presented?
I don't understand what do you mean.
If the CI853 is not exists, the redundancy doesn't work, because the communication fault on port CH3 does not switch the Controllers (stand-by - active) and I don't know if there is some instruction to do that via program.
I hope I helped you