This attribute is used to specify the reference designator to a
particular instantiated component. It must be on ALL
components which have some sort of electrical significance. This
attribute can also be on the inside of a symbol (it will be promoted,
i.e. attached to the outside of the symbol, if it is visible) to
provide a default refdes value (such as U?). Usually this
attribute is composed by a prefix (U for example) and a number
(different for each component).
Examples:
refdes=U1 refdes=R10 refdes=CONN1