The DINT typecast operator is used to convert an expression to a DINT type. If the typecast is used to convert from a "smaller" type, sign extension will occur.
Example:
INCLUDE rtcu.inc VAR a :INT; b :DINT; END_VAR; PROGRAM test; // Convert 'a' which is a INT type to a DINT (sign extension will occur) b :=DINT(a); END_PROGRAM;