Siemens SIMATIC S7 System Manual page 554

105BCommunication processor
12.3 Point-to-Point (PtP) communication
Parameter
Start on Any Character
Line Break
Idle Line
Special condition:
Recognize message start
with single character
Special condition:
Recognize message start
with a character sequence
The order of checking start conditions is:
● Idle line
● Line break
● Characters or character sequences
While checking for multiple start conditions, if one of the conditions is not met, the CM or CB
will restart the checking with the first required condition. After the CM or CB establishes that
the start conditions have been met, it begins evaluating end conditions.
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Definition
The Any Character condition specifies that any successfully received character indicates the
start of a message. This character is the first character within a message.
The Line Break conditions specifies that a message receive operation starts after a break
character is received.
The Idle Line condition specifies that a message reception starts once the receive line has
been idle or quiet for the number of specified bit times. Once this condition occurs, the start
of a message begins.
①
Characters
②
Restarts the idle line timer
③
Idle line is detected and message receive is started
Specifies that a particular character indicates the start of a message. This character is then
the first character within a message. Any character that is received before this specific
character is discarded. The default character is STX.
Specifies that a particular character sequence from up to four configured sequences
indicates the start of a message. For each sequence, you can specify up to five characters.
For each character position, you specify either a specific hex character, or that the character
is ignored in sequence matching (wild-card character). The last specific character of a
character sequence terminates that start condition sequence.
Incoming sequences are evaluated against the configured start conditions until a start
condition has been satisfied. Once the start sequence has been satisfied, evaluation of end
conditions begins.
You can configure up to four specific character sequences. You use a multiple-sequence
start condition when different sequences of characters can indicate the start of a message. If
any one of the character sequences is matched, the message is started.
S7-1200 Programmable controller
System Manual, 11/2011, A5E02486680-05