Siemens SIMATIC CP 340, Руководство пользователя

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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
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2.5.3 Receiving Data with the ASCII Driver
Selectable End Criteria
For data transmission using the ASCII driver you can choose between three different end
criteria. The end criterion defines when a complete message frame is received. The possible
end criteria are as follows:
●
Expiration of the character delay time
The message frame has neither a fixed length nor a defined end-of-text character; the
end of the message is defined by a pause on the line (expiration of character delay time).
● On Receipt of End Character(s)
The end of the message frame is marked by one or two defined end-of-text characters.
● On Receipt of Fixed Number of Characters
The length of the receive message frames is always identical.
Code transparency
The code transparency of the procedure depends on the choice of configured end criterion
and flow control:
●
With one or two end-of-text characters
–
not code-transparent
● When end criterion is character delay time or fixed message frame length
–
code-transparent
● Code-transparent operation is not possible when the flow control XON/XOFF is used.
Code-transparent means that any character combinations can occur in the user data without
the end criterion being recognized.