Shared variables work exactly as they were physical I/O's. However they are meant to be used as virtual I/Os in the following scopes:

• Inside signal flow diagrams.
• Amongst Finite States in Hierarchical State Machines.
• Amongst Tasks.

At the beginning of a task, values of shared variables are sampled from a memory table. The sampled values remain unchanged during the whole task execution. At the end of a task computation, the current values of the shared variables are updated into their memory table.

The diagram below can be used to illustrate the general process:

Figure 1 - Diagram using Shared Variable Input and Output blocks

Figure 2 - Simulation Information

In Figure 2, it is possible to see how long each block takes to be executed and complete the computation cycle:

• Sampling gets executed at first. This corresponds to the Shared Variable Input.
• It is followed by intermediate computation operations, when all the math blocks in Figure 1 get executed.
• Finally, the results get assignment to the Shared Variable Output block.

Three additional examples illustrate the most common principles applicable when using shared variables:

1. In signal flow diagrams: Shared Variable I/Os are not Goto and From blocks!
2. In Hierarchical State Machines: Conditional execution implies conditional memory table update.
3. Between tasks: priority-based execution assures predictable memory update.