Communication Between Compact Logix and Guard Logix Error

[parithielam15]

Hello Everyone,

I have a issue with communication between two different PLCs. So here is the facts, The Master PLC is Guard Logix 5069 with IP address 192.168.1.1. and we have a chiller with compact Logix (not sure of Model) with IP address 192.168.0.30.

Currently I am using the MODBUS TCP CLIENT AOIs available in Rockwell website, but it is Encountering a communication issue. The Modbus start to transfer the bit initially but after few minutes the module throughs, Overlap and Overload issue. which is breaks the steady communication. We tried to verify the polling interval at both end, and also increasing / decreasing the polling interval. Nothing works.


I tried to use the msg instruction, As it fails because of the IP.

Is there any solution for this Modbus client or can any suggest any other ways to attain an uninterrupted communication.

Thanks
EP

 

[dmroeder]

MSG instruction is the way. There is no reason to use Modbus when both PLC's already speak Ethernet I/P.

What is the subnet mask of both PLC's?

The keys to getting the MSG to work is both PLC's obviously need to be on the same same subnet. The configured path must be correct and data types in both PLC's need to match exactly.

 

[parithielam15]

Hi,

So the issue here is The supplier of the chiller doesn't need them to be in same subnet, i don't know the subnet of the compact Logix, but the subnet for the master PLC is 255.255.255.0.

So Modbus is not a right way to use as it is already in Ethernet protocol.

Can you say any idea for this,

And also can you comment on using the Gateway for data transfer.

Thanks

 

[robertmee]

Looks like the chiller address of 192.168.1.1 is just a default IP. Change it to the same IP subnet as the rest of the equipment and use a MSG instruction or produce/consume.

 

[Ken Roach]

A device with an IP address of 192.168.1.1 and subnet mask of 255.255.255.0 cannot communicate with a device with an IP address of 192.168.0.30 except through a router. They simply are not on the same IP subnet.

So you need to figure out your Ethernet infrastructure and connectivity. If there's a router or NAT device somewhere between these two controllers, you need to figure out how they are configured.

I agree that I would not try to use Modbus/TCP to communicate between two Rockwell Automation controllers. There's simply no reason to complicate the system when the two controllers support ordinary Tag read/writes natively.