Siemens Simatic S7-300 CP 341 User Manual page 66

Basic Principles of Serial Data Transmission
2.6 Data Transmission with the ASCII Driver
End criterion end-of-text character
When receiving data, the end of the message frame is recognized when the assigned end-
of-text character(s) are received. The received data including the endoftext character(s) are
accepted from the CPU.
If the character delay time expires while data is still being received, the receive operation is
ended. An error message is issued and the message frame fragment is discarded.
If you are working with endoftext characters, transmission is not code transparent. You must
then make sure that the end character(s) are not included in the user data of the user.
Note the following when the last character in the received message frame is not the end-of-
text character.
● End-of-text character elsewhere in the message frame:
All characters, including the end-of-text character, are written to the receive DB. The
characters located after the end-of-text character are
– Discarded if the character delay time expires at the end of the message frame.
– Merged with the next message frame if a new message frame is received before the
● End-of-text character not included in message frame:
The message frame is either:
– Discarded if the character delay time expires at the end of the message frame.
– Merged with the next message frame if a new message frame is received before the
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character delay time expires.
character delay time expires.
CP 341 Point-to-Point Communication, Installation and Parameter Assignment
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Manual, 09/2008, A5E02191071-01