Direct (Bit) Access on Variables

The IEC61131-3 Standard allows reading specific Bits, Bytes, Words or DWords from an ANY_BIT type. RuSTy supports this functionalty and extends it to support all INT types.

Constant based Direct Access

To access a bit sequence in a variable, a direct access instruction %<Type><Value> is used.

Type is the bit sequence size required and is described as follows:

For Bit access, the %X is optional.

Example

FUNCTION main : DINT
VAR
    variable    : LWORD;
    bitTarget   : BOOL;
    bitTarget2  : BOOL;
    byteTarget  : BYTE;
    wordTarget  : WORD;
    dwordTarget : DWORD;
END_VAR

variable    := 16#AB_CD_EF_12_34_56_78_90;
bitTarget   := variable.%X63; (*Access last bit*)
byteTarget  := variable.%B7; (*Access last byte*)
wordTarget  := variable.%W3; (*Access last word*)
dwordTarget := variable.%D1; (*Access last dword*)
(*Chaining an access is also allowed *)
bitTarget2  := variable.%D1.%W1.%B1.%X1;

END_FUNCTION

Varirable based Direct Access

While the IEC61131-3 Standard only defines variable access using constant int literals, RuSTy additionally supports access using Variables. The Syntax for a variable based access is %<Type><Variable>. The provided varibale has to be a direct Reference variable (non Qualified).

Short hand access for Bit (Without the %X modifier) is not allowed.

Example

FUNCTION main : DINT
VAR
    variable    : LWORD;
    access_var  : INT;
    bitTarget   : BOOL;
    bitTarget2  : BOOL;
    byteTarget  : BYTE;
    wordTarget  : WORD;
    dwordTarget : DWORD;
END_VAR
variable    := 16#AB_CD_EF_12_34_56_78_90;
access_var := 63;
bitTarget   := variable.%Xaccess_var; (*Access last bit*)
access_var := 7;
byteTarget  := variable.%Baccess_var; (*Access last byte*)
access_var := 3;
wordTarget  := variable.%Waccess_var; (*Access last word*)
access_var := 1;
dwordTarget := variable.%Daccess_var; (*Access last dword*)
(*Chaining an access is also allowed *)
bitTarget2  := variable.%Daccess_var.%Waccess_var.%Baccess_var.%Xaccess_var;
END_FUNCTION