I can assume that it's for the panel view?
This tends to show that there may be a basic misunderstanding in this process. The display asks the PLC for information and the PLC replies.
Here is a 'read' transaction put in people terms. The exact sequence and contents vary by the method of communication.
Display - "Hi there PLC. Can you give me the value which is as N7:4?"
PLC - "Certainly Display, the value at N7:4 is 42"
Display - "Thank You"
Sometimes a display page shows multiple items which are close together in memory locations. So something like this happens:
Display - "Hi there PLC. Can you give me the values which are in N7:10 through N7:19?"
PLC - "Certainly Display, the values for N7:10 through N7:19 are 12, 72, 183, 34, 519, 3, 22, 162, 9823 and 7640"
Display - "Thank you"
The display can also change values in the PLC:
Display - "Hi there PLC. I would like to change the value in N7:53 to 529"
PLC - "OK Display, I have changed the value in N7:53 to 529"
Display - "Thank you"
Actually the PLC has NO IDEA of the nature of the requesting device. The requester could be another PLC. It will respond to any properly formed request. On some communication types, for example Ethernet, multiple devices can communicate to the PLC. The nature of Ethernet (and other communication types) is that the request is tagged with the identification of the requester (IP) and the reply goes back to that particular requester.
I hope this helps.