Siemens SIMATIC CP 440 Manual page 35

The figure below illustrates a receive operation with the end criterion "end-of-text
character".
Figure 2-6
Point-to-point connection CP 440 Installation and Parameter Assignment
A5E00057742-02
Waiting for
character
Character
arrived
Character received
with end control
and character delay
time
Message
frame
complete
Message frame
entered in receive
buffer
Sequence of Receive Operation with End Criterion "End-of-Text Character"
Basic Principles of Serial Data Transmission
Error when receiving
Waiting for valid
end code
Expiration
of the
monitoring
time
Error entered in the
STATUS output of
the FB.
2-17