Hello

How can I decrease size of communication data buffer?

SM

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Split from work memory: communication data buffer .

https://support.industry.siemens.com/cs/ww/en/view/53843369 

Description
The size of the main memory of a SIMATIC CPU depends on the following parameter settings:

• Number of messages in the diagnostics buffer of the CPU
• Maximum number of communication jobs
• Size of the process-image input and output areas
• Amount of local data for all priority classes

It is particularly effective to change these parameters with CPU types that have small main memories.

A significant part of the main memory used by the CPU for programs is taken up by the diagnostics buffer of the CPU. Here you have to decide how many messages are required by your application in the diagnostics buffer.

Fig. 1: Setting options for the number of messages in the diagnostics buffer of the CPU

You can also change the number of communication jobs. You can read the requirement in your application in the "Communication jobs of which currently loaded" line (Fig. 4). Change the maximum number as necessary. Here, you must take into account a reserve of approx. 30% is achieved.
You can also change the message texts in this dialog.

Fig. 2: Communication job and local data setting options

If you pay attention to assign the IO addresses of the IO modules as far as possible without gaps, you can reduce the process image for inputs/outputs

Fig. 3: Setting options for the process image

You can see how the main memory is occupied online in the Properties of the CPU. In the "Memory" tab you select the field with the "main memory code" values (click in the field) and then click the "Main memory details" button.

https://www.automation.siemens.com/mdm/default.aspx?DocVersionId=23784500619&TopicId=19748299531

Hi 

You explain me how can I decrease communication job .I asked how can I decrease and control memory usage of communication data buffer. It seems it's allocated by firmware and I don't have any control on it.

SM