The syntax of an attribute is some named entity followed by an apostrophe and one of the following attribute names. A parameter list is used with some attributes.

Generally: **T** represents any type, **A** represents any array or constrained array type, **S** represents any signal and **E** represents a named entity.

T’BASE is the base type of the type T

T’LEFT is the leftmost value of type T. (Largest if downto)

T’RIGHT is the rightmost value of type T. (Smallest if downto)

T’HIGH is the highest value of type T.

T’LOW is the lowest value of type T.

T’ASCENDING is boolean true if range of T defined with to .

T’IMAGE(X) is a string representation of X that is of type T.

T’VALUE(X) is a value of type T converted from the string X.

T’POS(X) is the integer position of X in the discrete type T.

T’VAL(X) is the value of discrete type T at integer position X.

T’SUCC(X) is the value of discrete type T that is the successor of X.

T’PRED(X) is the value of discrete type T that is the predecessor of X.

T’LEFTOF(X) is the value of discrete type T that is left of X.

T’RIGHTOF(X) is the value of discrete type T that is right of X.

A’LEFT is the leftmost subscript of array A or constrained array type.

A’LEFT(N) is the leftmost subscript of dimension N of array A.

A’RIGHT is the rightmost subscript of array A or constrained array type.

A’RIGHT(N) is the rightmost subscript of dimension N of array A.

A’HIGH is the highest subscript of array A or constrained array type.

A’HIGH(N) is the highest subscript of dimension N of array A.

A’LOW is the lowest subscript of array A or constrained array type.

A’LOW(N) is the lowest subscript of dimension N of array A.

A’RANGE is the range A’LEFT to A’RIGHT or A’LEFT downto A’RIGHT .

A’RANGE(N) is the range of dimension N of A.

A’REVERSE_RANGE is the range of A with to and downto reversed.

A’REVERSE_RANGE(N) is the REVERSE_RANGE of dimension N of array A.

A’LENGTH is the integer value of the number of elements in array A.

A’LENGTH(N) is the number of elements of dimension N of array A.

A’ASCENDING is boolean true if range of A defined with to .

A’ASCENDING(N) is boolean true if dimension N of array A defined with to .

S’DELAYED(t) is the signal value of S at time now – t .

S’STABLE is true if no event is occurring on signal S.

S’STABLE(t) is true if no even has occurred on signal S for t units of time.

S’QUIET is true if signal S is quiet. (no event this simulation cycle)

S’QUIET(t) is true if signal S has been quiet for t units of time.

S’TRANSACTION is a bit signal, the inverse of previous value each cycle S is active.

S’EVENT is true if signal S has had an event this simulation cycle.

S’ACTIVE is true if signal S is active during current simulation cycle.

S’LAST_EVENT is the time since the last event on signal S.

S’LAST_ACTIVE is the time since signal S was last active.

S’LAST_VALUE is the previous value of signal S.

S’DRIVING is false only if the current driver of S is a null transaction.

S’DRIVING_VALUE is the current driving value of signal S.

E’SIMPLE_NAME is a string containing the name of entity E.

E’INSTANCE_NAME is a string containing the design hierarchy including E.

E’PATH_NAME is a string containing the design hierarchy of E to design root.