Rockwell Automation 1770, D17706.5.16 Ref Mnl DF1 Protocol Command - Manual (Page 60)

4–6 Using Full-duplex Protocol to Send and Receive Messages
Publication 1770Ć6.5.16 - October 1996
The following flowcharts the software logic for implementing the
transmitter:
Data DLE STX DLE ETX
BCC/CRC
Field
Received
DLE
ACK?
Timed
out?
3* NAKs
received
for this
message?
No No Received
DLE
NAK?
No
Yes Yes Yes
3* ENQ
sent?
P
P
T
T
T
= Ready to transmit next message
= Recovery procedure
= Default values used by the module
Yes Yes
No No
DLE ENQ
message frame
Legend:
retransmit same message
timeout loop
*
Important: Depending on network-link traffic and saturation level,
you may need to wait for a reply from the remote node
before transmitting the next message. Implement an
option that allows users to choose the maximum amount
of outstanding messages that can exist at one time;
we suggest a selectable range of one to three messages.