Download 1770-6.5.16, Front Cover

4–6
Using Full-duplex Protocol to Send and Receive Messages
The following flowcharts the software logic for implementing the
transmitter:
T
retransmit same message
message frame
DLE
STX
Data
DLE
ETX
BCC/CRC
Field
timeout loop
Received
DLE
ACK?
Yes
Legend:
T
= Ready to transmit next message
P
= Recovery procedure
*
= Default values used by the module
No
Received
DLE
NAK?
No
Timed
out?
Yes
Yes
T
3* NAKs
received
for this
message?
Yes
P
Yes
3* ENQ
sent?
No
No
DLE
Important:
Publication 17706.5.16 - October 1996
No
ENQ
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.