Siemens Simatic S7-400

Waiting for
character
Character received
with length control
and character delay
time
Message frame
entered in receive
buffer
Message
frame
complete
Character
arrived
Expiration
of the
monitoring
time
Waiting for
parameterized
number of characters
Error entered in the
STATUS output of
the FB.
Error when receiving
Message frame buffered
End criterion for message frame identified, error entry follows
Figure 2-7 Sequence of Receive Operation with "Fixed Message Frame Length" End Criterion
Receive Bu󹪜er on CP 440
The CP 440 receive bu󹪜er accommodates 2000 bytes. During the parameter assignment, you
can specify whether overwriting of data in the receive bu󹪜er should be prevented. You can also
specify the value range (1 to 10) for the number of bu󹪜ered receive message frames or use the
complete receive bu󹪜er.
You can delete the CP receive bu󹪜er at startup. You specify this setting either in the parameter
assignment screen or by calling the RES_RCV function block (see chapter "Communication via
Function Blocks (Page 73)").
Basic Principles of Serial Data Transmission
2.4 Data Transmission with the ASCII Driver
Point-to-point connection CP 440 Installation and Parameter Assignment
Equipment Manual, 03/2022, A5E00057742-AE 31