Technical data

Configuring Messages
16.1 The Message Concept
Programming with STEP 7
Manual, 05/2010, A5E02789666-01 339
16.1.5 Which Message Blocks Are Available?
You can choose between the following message blocks, each of which contains a programmed
message function:
• SFB 33: "ALARM"
• SFB 34: "ALARM_8"
• SFB 35 "ALARM_8P"
• SFB 36 "NOTIFY"
• SFC 18: "ALARM_S" and SFC 17: "ALARM_SQ"
• SFB 37: "AR_SEND" (for sending archives; no configuration of message texts and message
attributes possible)
• SFB 31: "NOTIFY_8P"
• SFC 107: "ALARM_DQ"
• SFC 108: "ALARM_D"
Details are found in the reference online help on blocks.
When to Use Which Message Block
The following table helps you decide which message block to choose for your particular task.
Selecting a message block depends on:
• The number of channels available in the block and therefore the number of signals that are
monitored with each block call
• Whether messages are to be acknowledged
• The option of also specifying associated values
• The display devices to be used
• The project data for the CPU to be used.
Message
Block
Chan-
nels
Acknow-
ledge-
ment
Asso-
ciated
Values
WinCC
Display
ProTool
Display
CPU
Messages
/S7 Status
Display
PLC Remarks
ALARM
SFB33
1 Possible Up to
10
Yes No No S7-400 Sends a
message for
each incoming or
outgoing edge
ALARM_8
SFB34
8 Possible No Yes No No S7-400 Sends a
message for
each incoming or
outgoing edge of
one or more
signals
ALARM_8P
SFB35
8 Possible Up to
10
Yes No No S7-400 As ALARM_8