Hi,
When a Constant block in Simulink has its sample time set to 'inf', it means the block has a constant sample time, which indicates that its output does not change during the simulation and is effectively constant for all time. However, even though the block value is constant, Simulink only produces an output at certain sample time hits during simulation.
For more information, refer to the following documentation link: http://www.ece.northwestern.edu/IT/local-apps/matlabhelp/toolbox/simulink/ug/how_simulink_works20.html
I hope this helps!
