Rockwell Automation 1770, D17706.5.16 Ref Mnl DF1 Protocol Command - Manual (Page 63)

4–9 Using Full-duplex Protocol to Send and Receive Messages
Publication 1770Ć6.5.16 - October 1996
The following flowchart is the software logic for implementing the
receiver.
Received
DLE
ENQ?
BCC/
CRC
OK?
Yes
No
Received
message?
No
No
Yes
Yes
RCVE
Send DLE LAST
LAST = ACK
LAST = NAK
LAST = NAK