Technical data

Generating Block-Related Messages
System Software for S7-300/400 System and Standard Functions - Volume 2/2
24-2 A5E00739858-01
Logging On Display Devices
Before SFBs for generating block-related messages can send a message when a
signal transition is detected, at least one display device (e.g. WinCC) must be
logged on for block-related messages. Parameter STATUS = 1 if no login exists.
Signal transition detection
One message memory with two memory blocks is available for each instance of a
message block.
This message memory is initially cleared. A signal transition at input SIG or at one
of the inputs SIG_1, ... SIG_8 is entered in the first memory block. This memory
block remains occupied until the corresponding message has been transferred.
The next signal transition detected at input SIG or at one of the inputs SIG_1, ...
SIG_8 is then entered in the second memory block. This second memory block will
always be overwritten if the first block is still occupied.
Output parameters ERROR and STATUS will indicate this loss of a message. This
information is also passed to the online displaying devices with the next message
that can be transferred.
After the first memory block is cleared, the data of the second memory block are
transferred to the first block. Thus, the second memory block is cleared again.
Acknowledgement triggered reporting
You can reduce message traffic on your system by operating the SFBs 33
"ALARM", 34 "ALARM_8" And 35 "ALARM_8P" with acknowledgement triggered
reporting.
That is, after an incoming message has been generated (Signal transition 0 > 1)
initially for a signal, subsequent messages will not be generated until you have
acknowledged the first message on a displaying device. The next message
displayed on the display unit after your acknowledgement ids the outgoing
message (Signal transition 1 to 0). The message cycle then restarts with an
incoming message (Signal transition 0 to 1) which must be acknowledged. by this
method you can use the display unit to control signal transition messages (save for
the outgoing message).
Set the reporting method (enable or disable acknowledgement triggered reporting)
for the SFBs 33 to 35 globally for the CPU in your STEP 7 configuration.
Acknowledgement triggered reporting is disabled by default.
To ensure consistent message evaluation within your system, you should verify
that all displaying devices can handle acknowledgement triggered reporting.
Note on operating displaying devices that can not handle acknowledgement
triggered reporting
A CPU with enabled acknowledgement triggered reporting will distribute the
messages only to displaying devices capable of handling this reporting method.
The CPU will not send any messages if none of the displaying devices can handle
acknowledgement triggered reporting. This situation is indicated once with
ERROR=1 and STATUS=1.