Receiving Data With The Ascii Driver - Siemens Simatic S7-300 CP 341 User Manual

Basic Principles of Serial Data Transmission
2.6 Data Transmission with the ASCII Driver
2.6.3

Receiving data with the ASCII driver

Receiving data with ASCII driver
For data transmission using the ASCII driver you can choose between three different end
criteria for data receipt. 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 a message frame is defined by a pause on the line (expiration of character delay
time).
● Receipt of the end-of-text character(s)
The end of the message frame is marked by one or two defined end-of-text characters.
● 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 the assigned end criterion
and the 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.
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CP 341 Point-to-Point Communication, Installation and Parameter Assignment
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Manual, 09/2008, A5E02191071-01