Technical data

Table Of Contents
Generating Block-Related Messages
System Software for S7-300/400 System and Standard Functions - Volume 2/2
A5E00739858-01
24-33
24.15 Generating Acknowledgeable and Permanently
Acknowledged Block Related Messages with SFCs 107
"ALARM_DQ" and 108 "ALARM_D"
Description
With every call the SFCs 107 "ALARM_DQ" and 108 "ALARM_D" generate a
message to which you can append an associated value. Thus, you correspond with
SFCs 17 "ALARM_SQ" and 18 "ALARM_S".
When generating messages with SFCs 107 "ALARM_DQ" and 108 "ALARM_D",
the operating system temporarily occupies a system resource for the duration of
the signal cycle.
The signal cycle time for SFC 108 "ALARM_D" starts at the SFC call with SIG=1
and ends at a new call with SIG=0. This interval for SFC 107 "ALARM_DQ" may be
extended by the time expiring until the incoming signal is acknowledged at a
logged in displaying device.
For SFC 108 "ALARM_D", the signal cycle lasts from the SFC call SIG=1 until
another call with SIG=0. For SFC 107 "ALARM_DQ", this time period also includes
the time until the incoming signal is acknowledged by one of the reported display
devices, if necessary.
If, during the signal cycle, the message-generating block is overloaded or deleted,
the associated system resource remains occupied until the next restart (warm
restart).
The additional functionality of SFCs 107 "ALARM_DQ" and 108 "ALARM_D"
compared to SFCs 17 and 18 is now that you can manage these occupied system
resources:
With the help of SFC 105 "READ_SI" you can fetch information related to
occupied system resources.
With SFC 106 "DEL_SI" you can release occupied system resources again.
This is of special significance for permanently occupied system resources. A
currently occupied system resource, for example, stays occupied until the next
restart (warm restart) if you, in the course of a program change, delete an FB
call that contains SFC107 or SFC108 calls . When you change the program,
and reload an FB with SFC 107 or SFC 108 calls, it may happen that the
SFCs 107 and 108 do not generate anymore messages.