Siemens SINUMERIK 840Di Function Manual page 1247

The structure of the machine data used is specified in a UDT:
TYPE UDT 20
END_TYPE
Note
ARRAY OF BOOL are always sent to even-numbered addresses. For this reason, an array
range of 0 to 15 must generally be selected in the UDT definition or all Boolean variables
specified individually.
Although only a REAL value is used initially in the example, a field (with one element) has
been created for the variable. This ensures that extensions can be made easily in the future
without the symbolic address being modified.
An entry is made in the symbol table to allow data access in symbolic form:
PLC Basic Program Solution Line (P3 sl)
Function Manual, 08/2005 Edition, 6FC5397-0BP10-0BA0
STRUCT
UDInt : ARRAY [0 .. 3 ] OF INT ;
UDHex0 : ARRAY [0 .. 15 ] OF BOOL ;
UDReal : ARRAY [0 .. 0 ] OF REAL ;
END_STRUCT;
2.7 Structure and functions of the basic program
//Description as field, for
// later expansions
Detailed Description
2-53