Siemens SIMATIC CP 440 Manual page 32

Basic Principles of Serial Data Transmission
Code Transparency
The code transparency of the procedure depends on the selection of the
parameterized end criterion and the flow control:
With one or two end-of-text characters
– Not code-transparent
When the end criterion is the character delay time or a fixed message frame
length
– Code-transparent
Code-transparent operation is not possible when XON/XOFF flow control is
used.
Code-transparent means that any character combination can occur in the user
data without the end criterion being detected.
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Point-to-point connection CP 440 Installation and Parameter Assignment
A5E00057742-02