Detects bit access to signed variables. However, the IEC 61131-3 standard permits only bit access and bit shift operations on bitfields. See also the strict rules SA0147 and SA0148.
Justification: Signed data types should not be used as bitfields and the other way around. The IEC 61131-3 standard does not provide for this kind of access, and therefore you should comply with this rule when you write portable code.
Importance: Medium
Exception for flag enumerations: When an enumeration is declared as a flag by means
of the {attribute 'flags'} pragma attribute, the SA0018 error is not issued for bit access with the OR, AND or NOT operators.
Example
PROGRAM PLC_PRG VAR iTemp1 : INT; diTemp3 : DINT; uliTemp4 : ULINT; siTemp5 : SINT; usiTemp6 : USINT; byTemp2 : BYTE; END_VAR iTemp1.3 := TRUE; // SA0018 diTemp3.4 := TRUE; // SA0018 uliTemp4.18 := FALSE; // no error because this is an unsigned data type siTemp5.2 := FALSE; // SA0018 usiTemp6.3 := TRUE; // no error because this is an unsigned data type byTemp2.5 := FALSE; // no error because the byte is a bitfield --> SA0018: Unusual bit access