The function generator can legitimately give discontinuous results. Sometimes, as in the case of "dead bands" this is intentional. When the input is in a particular range, the output is set to an arbitrary value (often 0.0) because the sensor simply is not workable at that range.
In physical processes, discontinuities are rare. In most F(x) blocks with discontinuities, there is actually an error, often a result of typographical mistakes.
Example:
F(x) discontinuity (step) in Module 1,16,06 Block 4216 at S8 X value of 460.000. ( S2, S3) 439.0 0.0 ( S4, S5) 440.0 150.0 ( S6, S7) 460.0 150.0 ( S8, S9) 460.0 143.0 (S10,S11) 480.0 143.0 (S12,S13) 480.0 143.0
The F(x) graph looks like this:
This error can be built directly into Hyperview. For more information, see the article Building error reports into the M14.