MATLAB: Do I receive an error message regarding output port required to be persistent when using Merge blocks in Simulink 7.0 (R2007b)

Question

In my model, I have a couple of Merge blocks feeding into another Merge block. The inputs to the Merge blocks are of Boolean data type and I have set the “Initial output” parameter of the Merge blocks to be [0]. However, when I update or simulate the attached model, I receive the following error message:

 The signal from 'testSimple/Merge' output port 1 is required to be persistent, hence this signal cannot be connected to a Merge block.

How do I resolve this issue?

Answer 1

The issue observed is because the output data type of the Merge blocks is Boolean. However, the "Initial Output” parameter for the Merge blocks is set to be "[0]" which is a double data type and hence the error message you receive.

In the help documentation for the Merge block (under "Guidelines for Using Merge Block"), it is mentioned "Always set the Initial output parameter of the Merge block, "unless" the output port of the Merge block connects to another Merge block".

So to resolve the issue, set the “Initial Output” parameter for the Merge blocks to be [].

The corrected model is attached.