Rockwell Automation 1770, D17706.5.16 Ref Mnl DF1 Protocol Command - Manual (Page 43)

3–6 Using Half-duplex Protocols to Send and Receive Messages
Publication 1770Ć6.5.16 - October 1996
The following flowchart shows the software logic for implementing
half-duplex protocol from the master node’s point of view:
Select node
Receive
DLE
EOT?
Message
OK?
No Yes
Receive
message?
No
No
No Yes
Does master
have message
to send?
XCVR
Yes
No
Send poll
Start timeout
Add node to
active list
Get message from
application layer
Yes
Duplicate
message?
Yes
Active
node?
No
Yes
Send message
Start timeout
No
3
timeouts
this
message?
Yes Tell application
layer of failure
Received
DLE
ACK?
No
3
timeouts
this poll?
Yes
No
Send message to
application layer
Send DLE ACK
No
Node
in active
list?
Yes
Yes
Send DLE ACK
Add node to
inactive list