Rockwell Automation 1770, D17706.5.16 Ref Mnl DF1 Protocol Command - Manual (Page 24)

1–7 Network Layers
Publication 1770Ć6.5.16 - October 1996
Your DF1 links and network links (DH, DH+, and DH485) each use
two layers of software to enable communication:
•
the data-link layer
•
the application layer
This figure shows how these layers fit together.
RSĆ232
data link
layer
common
application
routines
application
computer
DH/DH+/DH485
RSĆ232 interface modules
PLC processor
application
common
application
routines
DH/DH+
/DH485 data
link layer
link layer
(network)
link layer
(DF1)
RSĆ232 DH/DH+
DH485
DataĆlink Layer
This layer controls the flow of communication over the physical link
and:
•
determines the encoding of data on the physical medium
•
controls who transmits data and who listens using an
arbitration protocol
•
conveys data packets intact from the source node to the
destination node over the physical link
If your link is Then
a DH, DH+ or DH485 link
you do not need to program this layer.
Your application programs on the network
are not involved with interĆnode protocol,
handshaking, or control of the link.
a DF1 link between AllenĆBradley
interface modules
the interface modules automatically take
care of this layer. Your application
program does not have to be involved with
handshaking control.
a DF1 link between an AllenĆBradley
interface module and a computer
you must program this layer at your
computer.
Programming the data-link layer
You can program the data link layer using DF1 protocol.
For more information, see Chapter 3, “Using Half-duplex Protocol to
Send and Receive Messages,” or Chapter 4, “Using Full-duplex
Protocol to Send and Receive Messages.”
Software Layers
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