Siemens SIMATIC S7 System Manual page 254
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Point-to-Point (PtP) communications
8.7 Point-to-Point instructions
● Idle Line specifies that a message reception should start once the receive line has been
● Variable Sequences: Start conditions can be constructed that are based upon a variable
Start condition
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idle or quiet for the number of specified bit times. Once this condition occurs, the start of
a message will begin.
①
Characters
②
Restarts the idle line timer
③
Idle line is detected and message receive is started
number of character sequences (up to a maximum of 4) consisting of a varying number of
characters (up to a maximum of 5). Each character position within each sequence may
be selected as a specific character, or selected as a wild-card character, meaning any
character will qualify. This start condition can be used when different sequences of
characters indicate the start of a message.
Consider the following received hexadecimal coded message: "68 10 aa 68 bb 10 aa 16"
and the configured start sequences shown in the table below. Start sequences begin to
be evaluated when the first 68H character is successfully received. Upon successfully
receiving the fourth character (the second 68H), then start condition 1 is satisfied. Once
the start conditions are satisfied, the evaluation of the end conditions begins.
The start sequence processing can be terminated due to various parity, framing, or inter-
character timing errors. These errors result in no received message, because the start
condition was not satisfied.
First
Character
1
68H
2
10H
3
dcH
4
e5H
First Character
First Character
+1
+2
xx
xx
aaH
xx
aaH
xx
xx
xx
First Character
First Character
+3
+4
68H
xx
xx
xx
xx
xx
xx
xx
S7-1200 Programmable controller
System Manual, 11/2009, A5E02486680-02
- Quick Links:
- Introducing the S7-1200 Plc
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