Siemens SINUMERIK 828D Function Manual page 893

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.
Symbolic accesses
An entry is made in the symbol table to allow data access in symbolic form:
Symbol Operand
UData DB 20
Access operations in user program (list includes only symbolic read access):
...
L "UData".UDInt[0];
L "UData".UDInt[1];
L "UData".UDInt[2];
L "UData".UDInt[3];
U "UData".UDHex0[0];
U "UData".UDHex0[1];
U "UData".UDHex0[2];
U "UData".UDHex0[3];
U "UData".UDHex0[4];
U "UData".UDHex0[5];
U "UData".UDHex0[6];
U "UData".UDHex0[7];
... ...
U "UData".UDHex0[15];
L "UData".UDReal[0];
...
Basic Functions
Function Manual, 09/2011, 6FC5397-0BP40-2BA0
P3: Basic PLC Program for SINUMERIK 840D sl
13.8 Structure and functions of the basic program
Data type
UDT 20
893