Multi-instances
Definition
When a function block (FB) calls another FB, its instance data can also be stored in the instance DB of the calling FB. This type of block call is referred to as a multi-instance.
Advantages
The use of multi-instances provides the following advantages:
Good structuring options for complex blocks
Lower number of instance DBs
Easy programming of local subprograms, for example for local timers or edge evaluations.
How multi-instances work
The following figure shows an FB that uses another FB ("Valve"). "Valve" is called as a multi-instance, i.e. it stores its data in the instance DB of the calling FB. Multi-instance data is located in the "Static" section of the calling block. In CPUs of the S7-1200/S7-1500 series, the instance can also be located in the instance DB of another function block.
Creating multi-instances
You have the following options for creating a multi-instance:
When you call an FB in the program, the "Call options" dialog appears. Here, you can specify whether you want to call the FB as a single instance, multi-instance or parameter instance.
You declare the multi-instance directly in the interface of the calling block.
You declare the multi-instance in the interface of another function block (S7-1200/S7-1500).
See also: Declaring multi-instances
ARRAYs of multi-instances
Multi-instances can also be created as an ARRAY. You can address the individual ARRAY elements using a variable index, for example when processing program loops.
You declare ARRAYs of multi-instances directly in the interface of a function block.
Calling multi-instances
When a multi-instance is called, the assigned instance is indicated. The following figures show the call of the "Block" block as a multi-instance in LAD.
In the following example, the instance is located locally in the instance DB of the calling block:
In the following example, the instance is located in the instance DB "MyOtherFB" (S7-1200/S7-1500):
In the following example, the instance is located in an ARRAY of multi-instances in instance DB "MyOtherFB" (S7-1200/S7-1500):
Note
Calling and addressing blocks in namespaces
Blocks located in namespaces are represented in the program code in IEC-compliant notation:
The block name is not in quotation marks.
The namespace precedes the block name, separated by a dot.
You can find detailed information on the notation of namespaces under: Introduction to namespaces
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See also
Instance data blocks
Basics of instances
Single instances
Example of using parameter instances in an ARRAY of multi-instances
EMERSON EDUARDO RODRIGUES
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