Siemens SIMATIC CP 340 - Page 54

Basic Principles of Serial Data Transmission
2.5 Data transfer using the ASCII driver
PtP coupling and configuration of CP 340
54 Manual, 04/2011, A5E00369892-03
End Criterion Fixed Message Frame Length
When data is received, the end of the message frame is recognized when the configured
number of characters has arrived. The received data is taken over by the CPU with the
function block P_RCV.
If the character delay time expires before the configured number of characters has been
reached, the receive operation is terminated. An error message is issued and the message
frame fragment is discarded.
The figure below illustrates a receive operation with the end criterion "Fixed message frame
length".
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Figure 2-17 Sequence of Receive Operation with End Criterion "fixed message frame length"