The Hysteresis block is a very simple hysteretic quantisation function that maps the trajectory of the input function to only two values (yL and yU). However, the resulting quantisation function is hysteretic: when the input function crosses the value xU from below, the block produces an output of the value yU. Analogously, when the signal crosses xL from above, the Hysteresis block produces an output with the value yL. If the signal crosses either xU from above or xL from below, nothing happens. This means in particular that the input function can take the same value twice, each time though triggering a different output event.
See also the Quantised State Systems section for more details about hysteretic quantisation functions.
The following picture shows an input function in the form of a sine signal (blue) and the output of the Hysteresis block (red) with the following parameter setting: xU =1.5, xL =-1, yU =0.5 and yL =-0.5.
.ModelicaDEVS.FunctionBlocks.Hysteresis