Siemens S7-1200 System Manual page 691

Parameter and type
SEQ[1].CTL
SEQ[1].STR
SEQ[2].CTL
SEQ[2].STR
SEQ[3].CTL
SEQ[3].STR
SEQ[4].CTL
SEQ[4].STR
Example
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.
Table 12- 16 Start conditions
Start condition First Character
1 68H
2 10H
3 dcH
4 e5H
S7-1200 Programmable controller
System Manual, 03/2014, A5E02486680-AG
Data type
IN Byte
IN Char[5]
IN Byte
IN Char[5]
IN Byte
IN Char[5]
IN Byte
IN Char[5]
First Character +1
xx
aaH
aaH
xx
Communication processor and Modbus TCP
Description
Sequence 1 ignore/compare control for each character: (Default
value: B#16#0)
These are the enabling bits for each character in start sequence
01H - Character 1
•
02H - Character 2
•
04H - Character 3
•
08H - Character 4
•
10H - Character 5
•
Disabling the bit associated with a character means any character
will match, in this sequence position.
Sequence 1 start characters (5 characters). Default value: 0
Sequence 2 ignore/compare control for each character. Default
value: B#16#0)
Sequence 2 start characters (5 characters). Default value: 0
Sequence 3 ignore/compare control for each character. Default
value: B#16#0
Sequence 3 start characters (5 characters). Default value: 0
Sequence 4 ignore/compare control for each character. Default
value: B#16#0
Sequence 4 start characters (5 characters), Default value: 0
First Character +2
xx
xx
xx
xx
12.3 Point-to-point (PtP) communication
First Character +3 First Character +4
68H xx
xx xx
xx xx
xx xx
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