Rockwell-automation 1770, D17706.5.16 Ref Mnl DF1 Protocol Command Manuel d'utilisateur Page 57

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4–3Using Full-duplex Protocol to Send and Receive Messages
Publication
17706.5.16 - October 1996
Figure 4.2
Software implementation of data paths
Software
Multiplexer
To implement four logical paths with two physical circuits, a software multiplexer is needed to combine the message symbols with
the response symbols going in the same direction.
At the other end of the link, a software separator divides the message symbols from the response symbols.
The internal software sends the message symbols to the appropriate receiver, and the response symbols to the appropriate
transmitter.
Although message symbols and response symbols on the same circuit operate independently of each other,
there is some interaction.
For example, a message on physical circuit AB will be delayed if a response symbol from receiver A is inserted in a stream of
message symbols from transmitter A (embedded response).
Also, any hardware problems that affect message symbols traveling over a circuit will also affect response symbols
on the same circuit.
Transmitter A
Receiver B
Path 1
Path 2
Physical Circuit AB
Path 2
Path 1
Physical Circuit BA
Software
Multiplexer
Path 3 Path 4Path 4 Path 3
Transmitter B
Software
Separator
Receiver A
Software
Separator
Paths 1, 2, 3, and 4
Paths 1 (a message symbol sent from node A to node B)
Software
Multiplexer
Transmitter A
Software
Separator
Receiver B
Path 1
Path 1
Physical Circuit
To define the environment of the protocol:
the transmitter needs to know where to get the message it sends,
the message source. We assume the message source:
supplies one message at a time upon request from the
transmitter
requires notification of the success or failure of the transfer
before supplying the next message
the receiver must have a means of disposing of messages,
the message sink
If the Then the
message source is empty
transmitter waits in an inactive state until a
message is available
receiver has received a message
successfully
receiver attempts to give it to the message
sink. If the message sink is full, the
receiver must be notified
Fullduplex Protocol
Environment
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