Technical data

Table Of Contents
Generating Block-Related Messages
System Software for S7-300/400 System and Standard Functions - Volume 2/2
24-26
A5E00739858-01
24.12 Introduction to Generating Block-Related Messages
with SFCs
SFCs for Generating Block-Related Messages
You can generate a block-related message with the following SFCs:
SFC 17 "ALARM_SQ"
SFC 18 "ALARM_S"
SFC 107 "ALARM_DQ"
SFC 108 "ALARM_D"
These SFCs have the following properties:
The messages sent by SFC 17 "ALARM_SQ" and SFC 107 "ALARM_DQ"
when the signal state is 1 can be acknowledged at a logged on display device.
The messages of SFC 18 "ALARM_S" and SFC 108 "ALARM_D" are always
implicitly acknowledged. It is not a detected edge change that generates a
message but rather each SFC call. For more detailed information refer to
Generating Acknowledgeable Block-Related Messages with SFC 17
"ALARM_SQ" and Permanently Acknowledged Block-Related Messages with
SFC 18 "ALARM_S"
"ALARM_S" and the section Generating Acknowledgeable Block-Related
Messages with the SFCs 17 "ALARM_DQ" and 108 "ALARM_D".
Following execution of the block, the associated value SD_1 is read completely
and assigned to the message. In terms of consistency compared with high-
priority classes, the following associated values are consistent:
- the simple data types (bit, byte, word, and double word)
- an array of the data type byte up to a maximum length specific to the
particular CPU (see /71/, /101/).
SFC 19 "ALARM_SC"
Using SFC 19 "ALARM_SC" you can query the following:
The acknowledgment status of the last "entering state message" and the signal
state at the last SFC 17/SFC 107 call, or
The signal state at the last SFC 18/SFC 108 call.
Logging On Display Devices
The SFCs for generating block-related messages only send a message when they
are called if at least one display device has logged on for block-related messages.