Rockwell-automation 1770, D17706.5.16 Ref Mnl DF1 Protocol Command Uživatelský manuál Strana 24

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1–7Network Layers
Publication
17706.5.16 - 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.
RS232
data link
layer
common
application
routines
application
computer
DH/DH+/DH485
RS232 interface modules
PLC processor
application
common
application
routines
DH/DH+
/DH485 data
link layer
link layer
(network)
link layer
(DF1)
RS232 DH/DH+
DH485
Datalink 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 internode protocol,
handshaking, or control of the link.
a DF1 link between AllenBradley
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 AllenBradley
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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