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Entry type: FAQ, Entry ID: 23730649, Entry date: 06/29/2015

How do you implement chronological messaging with S7-300 CPUs and WinCC?

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This entry shows you how to implement chronological messaging with an S7-300 CPU and WinCC.

Chronological messaging means that the messages are sent from the PLC to the WinCC station. When they are created in the PLC, the messages are given a time stamp and sent to the WinCC station. The WinCC station does not need to poll the PLC. This significantly reduces the bus load. There are two types of message in STEP 7 :

  1. Symbol-related messages
  2. Block-related messages

You can configure only block-related messages for an S7-300 CPU. These block-related messages are created by the STEP 7 program with the aid of the system message blocks. The message is sent as soon as the STEP 7 program calls a system message block and the conditions for sending a message are fulfilled. The messages are triggered synchronously to the program. The system message blocks SFC17 (ALARM_SQ), SFC18 (ALARM_S), SFC107 (ALARM_DQ) and SFC108 (ALARM_D) can be used in an S7-300 CPU (CPU 314 onwards) for block-related messages. In contrast to ALARM_S/SQ, ALARM_D/DQ offers possibilities for managing your system resources; otherwise, they are identical. The S7-312 and S7-313 CPUs do not support these system message blocks!

Further Information

  • Manual "SIMATIC S7-300 CPU 31xC and CPU 31x, Technical Data"
    This provides detailed information about the performance data of the available alarm processes of a CPU - Entry ID 12996906
  • Manual "Operation List CPU 31xC, CPU 31x, IM 151-7 CPU, IM 154-8 CPU, BM 147-1 CPU, BM 147-2 CPU"
    This provides detailed information about available system functions and system function blocks for creating CPU messages - Entry ID 13206730.
  • STEP 7 Online Help
    You can find detailed information about alarm processes, alarm types and system alarm blocks in the STEP 7 Online Help under "Configuring Messages". You can obtain detailed information if you install the block in the program and press the F1 key.


  • The WinCC component "AS-OS Engineering" is installed.
    You can select this component when doing a user-defined setup of WinCC. Please use the following installation sequence:
    1. STEP 7
    2. WinCC with the "AS-OS Engineering" component

    Entry 22272911 includes a description of how to retro-install the "AS-OS Engineering" component.

  • The WinCC project is integrated in the STEP 7 project.
    Entry ID 11841504 contains information on how to integrate a WinCC project in STEP 7.
  • The "Alarm Logging Runtime" is enabled in the startup list in the "Computer Properties" dialog of the WinCC project.

Below is a description of how to configure block-related messaging.

Configuring block-related messages
Here we present block-related messaging using the
system message block SFC17 (ALARM_SQ). The procedure using the system message block SFC18 is essentially identical. Two messages are configured in one function block.

No. Procedure
1 Copy SFC17 (ALARM_SQ) into the current project
In the SIMATIC Manager you select "File > Open... > Libraries" and open the Standard Library. Select the system message block SFC17 (ALARM_SQ). It is located in the directory "Standard Library > System Function Blocks > Blocks". Copy the system message block SFC17 into the project.
2 Create a message-compatible block
  • Insert a new function block into the STEP 7 project, "FB1", for example. The language used is STL.
  • Open the function block "FB1".
  • Create the following input variables:
    EV_ID1 (DWORD)
    EV_ID2 (DWORD)
    SIG1 (BOOL)
    SIG2 (BOOL)
    SD1 (WORD)
    SD2 (WORD)
  • Create the following output variables:
    RET_VAL1 (INT)
    RET_VAL2 (INT)
  • Create the following temporary variable
    RET_iVal (INT)
  • Open the "Variable Properties" dialog of input "EV_ID1". Assign the following attributes:
    S7_a_type = alarm_s
    S7_server = alarm_archiv

    Fig. 01
  • Repeat the procedure of the previous step for input "EV_ID2".
  • Select the system message block SFC17 (ALARM_SQ) in the program part. Connect the parameters of the system message block with the corresponding inputs/outputs of the function block.

    Fig. 02

    The "ID" parameter is permanently set with the value "W#16#EEEE".
    The SIG parameter triggers the message.
    The EV_ID parameter receives the message number generated by the system.
    With the SD parameter you can configure a message-associated value.
    The RET_VAL parameter contains error information.
  • Call SFC17 a second time, because you can only monitor one message variable with this block. Make the relevant settings as described in the point above.
  • Save the function block FB1 and close the editor.
3 Configure standard messages
Select function block "FB1" in the SIMATIC Manager. In the pop-up menu you call the command "Special Object Properties > Messages...".
The Message Configuration dialog opens.

Fig. 03

Specify the message text for the messages EV_ID1 and EV_ID2.

It is also possible to configure the message texts in multiple languages. The display language currently selected is shown in the "Message Configuration" dialog. You must configure the message texts for all those languages that will be used later for WinCC Runtime. For this you change the standard language in the SIMATIC Manager with the menu command "Options > Language for Display Devices" and repeat the message configuration for each language separately.

4 Call message-compatible block in the program
Call message-compatible block in the program. For this you open the organization block OB1 and enter the following code:

Fig. 04

The IDs for the messages are generated automatically by STEP 7. You must not change these IDs!

Save the organization block OB1 and close the editor.

5 Configure block-related messages
After incorporating the message-compatible block you can change the message texts. For example, you can extend the message text by adding the actual name of the measuring point. For this you mark the instance data block in the SIMATIC Manager, "DB1", for example. In the pop-up menu you call the command "Special Object Properties > Messages...".
The Message Configuration dialog opens. Change the message text accordingly for each relevant language.

Fig. 05
6 Download program in PLC
Download the program into the PLC.
7 Compile OS
"OS Compile" creates the messages in WinCC. In earlier versions the procedure was also done with "Mapping" or "Transfer PLC/OS Connection Data".

The PLC's CPU and the OS must be networked. There must be at least one common network connection in NetPro.

Fig. 06

Fig. 07

A wizard takes you through multiple dialogs. Here you can make various settings for compiling the OS. You must select which PLC program is assigned to which OS and which connection is to be used.

Using the "Back" and "Next" buttons you can navigate in the wizard's settings mask. With the "Finish" button you get a summary of the compilation procedure displayed. Start compilation with the "Compile" button.

8 OS download
Download the program into the OS.
9 Test the messages at WinCC Runtime
Start WinCC Runtime. Trigger the messages using the variable table. The messages are displayed in the alarm window of WinCC and can be acknowledged where necessary. You can diagnose the messages alternatively with the STEP 7 program "CPU Messaging".

Fig. 08

The STEP 7 dialog "Message Configuration" makes the column "Message text" available by default in the Alarm Logging Editor. The texts in the "Message text" column are saved in the User text block 3(event) of a message.

Further information about the assignment of the STEP 7 message texts to the WinCC user text blocks is available in Entry ID: 30550239.

This entry was created with WinCC V6.0 SP4  and STEP 7 V5.3 SP2.

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