Technical data

Table Of Contents
Generating Block-Related Messages
System Software for S7-300/400 System and Standard Functions - Volume 2/2
24-30
A5E00739858-01
Acknowledging Messages
You can acknowledge messages sent by SFC 17 "ALARM_SQ" when the state of
the monitored signal is 1. You can query the acknowledgment status of the last
"entering event message" and the signal state at the last SFC call using SFC 19
"ALARM_SC." Messages you have sent with SFC 18 "ALARM_S" are always
implicitly acknowledged. You can query the signal state at the last SFC 18 call
using SFC 19 "ALARM_SC."
Temporary Storage of Signal States
SFC 17 "ALARM_SQ" and SFC 18 "ALARM_S" temporarily occupy system
resources. Here, they enter among other things the last two signal states including
the time stamp and associated value. If SFC 17 or SFC 18 is called at a time when
the signal states of the two last "valid" SFC calls have not yet been sent (signal
overflow), the current and the last signal state are discarded and an overflow ID is
set in the buffer. At the next possible opportunity, the second but last signal and the
overflow identifier are sent.
Example:
t
t 1 t 2t 0
t0, t1 and t2 are the points at which SFC 17 or SFC 18 are called. If the signal
states of t0 and t1 are not sent at the time t2, the signal states of t1 and t2 are
discarded and the overflow identifier is set for the signal state of t0.