Rockwell Automation 1770, D17706.5.16 Ref Mnl DF1 Protocol Command - Manual (Page 25)

1–8 Network Layers
Publication 1770Ć6.5.16 - October 1996
Application Layer
This layer controls and executes the actual commands specified in
the communication between nodes. This layer is the same for both
DF1 and network links. The application layer:
•
interfaces to user processes and databases
•
interprets commands
•
formats user data into packets
The application layer depends upon the type of node the application
is running on since it must interface to the user process and interpret
the user database.
Processes in the application layer
The application layer is typically organized into two types of
processes:
•
senders — A sender, after receiving a signal from the user
process, sends a message and awaits a reply. It then sends the
results to the user process.
•
responders — A responder waits for an incoming message from
the link. When the responder receives a message, it performs the
indicated operation on the user data base and returns a reply
message to the sender.
If your physical link is Then
a network link
the communication modules automatically
take care of this layer.
a DF1 link between AllenĆBradley interface
modules
the interface modules automatically take
care of this layer. (See figure below.)
PLCĆ5/15
processor
SLC 5/02
processor
1747ĆKE
RSĆ232
DF1 fullĆduplex
DH+ link
DH485 link
1785ĆKE
a DF1 link between an AllenĆBradley
interface module and a computer
you will need to program this layer at your
computer.
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