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Entry type: FAQ Entry ID: 98699910, Entry date: 08/16/2021

Which quantity framework must you pay attention to for communication between an S7-1200 or S7-1500 controller and WinCC Runtime Professional?

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If WinCC Runtime Professional is connected with an S7-1200 / S7-1500, you can only use the software effectively if the defined quantity framework per S7 is not exceeded. This entry shows the quantity frameworks for tags whose values are supplied by an S7-1200 / S7-1500.

The terms "Plc Attributes (max)" and "Minimum Plc Attributes (free)" are defined by the "WinCC Channel Diagnosis" tool (see Fig. 01). "Plc Attributes (max)" is the maximum number of tags that can be read by means of subscriptions with a cycle of less than 5 seconds.

It is generally assumed that the communication load of the S7 is not configured under 30% (default value: 50%). The values specified for "Minimum Plc Attributes (free)" are not precise, but only values based on experience. This number is valid for the engaged status, without screen change. Therefore, the minimum number ("Minimum Plc Attributes (free)") may be temporarily lower; as soon as the number tends towards 0, the cyclic reading with low cycle times (less than 5 seconds) starts, which means that the communication to the S7 might be temporarily overloaded.
The "Plc Attributes" can be used by one or multiple WinCC Runtime systems. Therefore, the number of tags logged on simultaneously per S7 of all the connected WinCC Runtime systems is to be added. How to determine the number of tags logged on simultaneously is described in the following under "Essential influencing factors for tags logged on simultaneously".



  • The information in the PDF files always refers to WinCC Professional that is connected with a CPU of a specific version of TIA Portal. This means that WinCC Professional V15.1 can also connect with a CPU of TIA Portal versions V15.1, V15, V14, and V13.
  • The firmware version has been added in the PDF files for V15 and V15.1. With TIA Portal V15 and higher you can select the firmware version of the CPU.
  • To ensure stable communication with the S7 you should not exceed the "Number of tags logged on simultaneously per S7".
  • Always use the current firmware of the CPUs to access the specified data. The current firmware is available in the Online Portal by entering the article number of your CPU and selecting the Entry Type "Download".

Determining the current values
The "Number of WinCC Runtime Professional systems" indicates the maximum number of WinCC Runtime Professional systems that can connect to one S7. The number takes into account the fact that one WinCC ES has connected to the S7 at the same time.
You should use the "WinCC Channel Diagnosis" tool to determine all the other current values.


Fig. 1

The values for the "Plc Attributes (max)" and "Minimum Plc Attributes (free)" columns of the tables can be read from "WinCC Channel Diagnosis" under "CCS7PLUSCHANNEL" and the corresponding connection. The number of tags logged on simultaneously per S7 can be determined by the "Plc Tag Subscriptions" (cyclic service) counter: The number of tags logged on per cycle time is displayed. In the example below the number is 2003 (500 ms: 103 tags, 1 s: 400 tags, 2 s: 500 tags, 5 s: 1000 tags).

Fig. 2

Essential influencing factors for tags logged on simultaneously
The number of tags logged on simultaneously is determined according to the table below. Here, the cycle times of less or equal to 5 seconds are relevant. Generally only the tags acquired by an S7 are relevant. In the "Channel Diagnosis" example above, these are the tags of the "PLC1516" connection.

Function Tags logged on simultaneously
Archiving  Sum of all tags per acquisition cycle.
HMI messages Number of tags for bit alarms + number tags for analog alarms + number of associated values from tags per alarm.
Scheduler Sum of all the tags used per cyclic event; with SmartTags only the SmartTags with cache utilization are relevant.
Number of trigger tags used.
Scripts This concerns cyclic scripts and the functions there which use a cache; notes on the utilization of caches is available in the documentation. Examples:
• HmiRuntime.Tags().Read 0
• SmartTags when using the cache
All tags concerned are included in the count.
Screen Number of tags directly linked to object properties
Number of tags used directly in controls with cycles (gage control, trend displays, table displays, for example)
Number of tags in cyclic animations, CScripts, VBScripts
Number of trigger tags used.
OPC server
(DA / UA)
Sum of all items logged on cyclically
Control Development Sum of all tags read cyclically
Table 1

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