SA0028: Overlapping memory areas

Function	Determines the points due to which two or more variables occupy the same storage space.
Reason	If two variables occupy the same storage space, the code may behave very unexpectedly. This must be avoided in all cases. If the use of a value in different interpretations is unavoidable, for example once as DINT and once as REAL, you should define a UNION. Also, via a pointer you can access a value typed otherwise without converting the value.
Importance	High

Sample:

In the following sample both variables use byte 21, i.e. the memory areas of the variables overlap.

PROGRAM MAIN
VAR
    nVar1 AT%QB21  : INT;        // => SA0028 
    nVar2 AT%QD5   : DWORD;      // => SA0028 
END_VAR