How can I read from Compactlogix to PLC-5 through ethernet (same network). I'm using the MSG instruction but PLC-5 won't read a 'tag' from Compactlogix, right? Thanks!
There is
no way a PLC5 will "read" a ControlLogix tag, it just doesn't understand the much newer ControlLogix tag database concepts, and RA will never put that functionality into the PLC5.
Instead, they have provided a mechanism in the ControlLogix that provides compatability with the older systems like PLC5 and SLC PLCs.
This mechanism allows the PLC5 or SLC to "believe" it is reading a data-table address from another PLC5 or SLC. And that is where the "Map PLC5/SLC Messages" comes into play in the ControlLogix project. (Find Map PLC5/SLC Messages" under the "Logic" menu).
Example :-
For simplicity, I will describe reading a ControlLogix INT array called CLX_Data, which will be 20 INTs in length.
The PLC5 message will have to be set-up to read a valid PLC5 data-table address, e.g. N120:0 length 20
The ControlLogix will have to have added to the "Map PLC5/SLC Messages" the following association - File Number = 120 ControlLogix Tag = CLX_Data. Then whenever the ControlLogix sees a message for read or write access to N120, it substitutes CLX_Data to access the data. Therefore, if the message tries to read N120:6, length 3, the mapping supplies the data from CLX_Data[6], length 3
Personally, I think that it is
easier to let the ControlLogix handle data-transfers to/from legacy PLCs and SLCs. No mapping is required, the message configuration directly specifies the source/destination data-table addresses.