The operator is an extension of the IEC 61131-3 standard.
BITADR yields the bit offset within a segment in a DWORD.
NOTICE
The offset depends on whether the "Byte addressing" option is selected or cleared in the target system settings.
The highest value nibble (4 bits) in this DWORD defines the memory range:
Marker M: 16#40000000
Input I: 16#80000000
Output Q: 16#C0000000
CAUTION
When using pointers to addresses, note that applying an online change can shift the contents of addresses.
Example
ST implementation language:
VAR
xVar AT %IX2.3 : BOOL;
dwBitoffset : DWORD;
END_VAR
dwBitoffset := BITADR(xVar); (* If byte addressing = TRUE, result = 16#80000013; if byte addressing = FALSE, result = 16#80000023 *)