Technical data

Configuring Messages
16.1 The Message Concept
Programming with STEP 7
Manual, 05/2010, A5E02789666-01 335
16.1.2 Choosing a Messaging Method
Overview
The following table shows the properties and requirements for the different messaging methods:
Message Numbering
• Messages are managed in a common database for
programming device and operator panel
• The load on the bus is low (programmable controller
signals active)
• Messages receive the timestamp from the
programmable controller
Bit Messaging
• There is no common database for the
programming device and operator panel
• The load on the bus is high (operator panel
polls)
• Messages receive the timestamp from the
operator panel
The message numbering method recognizes the following three types of messages:
Block-Related Messages Symbol-Related Messages User-Defined Diagnostic Messages
• Synchronized with the
program
• Displayed by ProTool (only
ALARM_S) and WinCC
• Possible with S7-300/400
• Programming using message
blocks:
- ALARM (S7-400 only)
- ALARM_8 (S7-400 only)
- ALARM_8P (S7-400
only)
- NOTIFY (S7-400 only)
- NOTIFY_8P (S7-400
only)
- ALARM_S(Q)
- AR_SEND (S7-400 only)
- ALARM_D(Q)
• Transfer to the operator
control system
- for WinCC via
AS-OS engineering
- For ProTool using
ProTool functions
• Not synchronized with the
program
• Display by WinCC
• Only possible with S7-400
• Configuration using the
symbol table
• Transfer to the AS
using system data
blocks (SDBs)
• Transfer to
operator control system
using AS-OS engineering
• Synchronized with the program
• Display in the diagnostic buffer
on the PG
• Possible with S7-300/400
• Programming using message
block (system function)
- WR_USMSG
• No transfer to operator control
system
STEP 7 only supports the more user-friendly message numbering method which will be described
in detail below. Bit messaging is configured in the HMI devices and is described there.