Rockwell Automation 1770, D17706.5.16 Ref Mnl DF1 Protocol Command - Manual (Page 61)

4–7 Using Full-duplex Protocol to Send and Receive Messages
Publication 1770Ć6.5.16 - October 1996
How the Receiver Operates
The receiver must be capable of responding to adverse situations.
Some of the problems that can occur are:
•
the message sink is full, so the receiver has nowhere to put
a message
•
a message can contain a parity error
•
the BCC or CRC can be invalid
•
the DLE STX or DLE ETX BCC/CRC may be missing
•
the message is too long or too short
•
a false control or data symbol occurs outside a message
•
a false control symbol occurs inside a message
•
the DLE ACK response is lost, causing the transmitter to send a
duplicate copy of a message already passed to the message sink