Siemens SIMATIC CP 340 - Page 53

Basic Principles of Serial Data Transmission
2.5 Data transfer using the ASCII driver
PtP coupling and configuration of CP 340
Manual, 04/2011, A5E00369892-03
53
End Criterion End-of-Text Character
When data is received, the end of the message frame is recognized when the configured
end-of-text character(s) arrive. The received data, including the end-of-text character, is
taken over by the CPU with the function block P_RCV.
If the character delay time expires while the message frame is being received, the receive
operation is terminated. An error message is issued and the message frame fragment is
discarded.
If you are working with end-of-text characters, transmission is not code-transparent, and you
must make sure that the end code(s) do not appear in the user data of the user.
The figure below illustrates a receive operation with the end criterion "End-of-text character".
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:DLWLQJIRU
FKDUDFWHU
&KDUDFWHUUHFHLYHG
ZLWKHQGFRQWURO
DQGFKDUDFWHUGHOD\
WLPH
0HVVDJHIUDPH
HQWHUHGLQ
UHFHLYHEXIIHU

0HVVDJH
IUDPH
FRPSOHWH
&KDUDFWHU
DUULYHG
&KDUDFWHU
GHOD\WLPH
H[SLUHG
:DLWLQJIRUYDOLG
HQGFRGHRUH[SLUDWLRQRI
FKDUDFWHUGHOD\
(UURUHQWHUHGLQ
UHFHLYHEXIIHU
(UURUZKHQUHFHLYLQJ
0HVVDJHIUDPHEXIIHUHG
(QGFULWHULRQIRUPHVVDJHIUDPHLGHQWLILHGHUURUHQWU\IROORZV
Figure 2-16 Sequence of Receive Operation with End Criterion "End-of-Text Character"