The stack is composed by a number of levels, each one capable of storing a single object. Since the stack is the place where data is created, manipulated and computed, its importance is paramount and unsurprisingly many commands are devoted to move, duplicate and delete data on the stack.
newRPL operates the stack in three different modes which differ by the number of levels and the mechanics of the stack movements:
RPL mode has been introduced by the HP28C/S calculator and used in all following calculators up to the HP50g. It is characterized by a stack with a number of levels limited only by the available memory. The lack of a top level simplifies somewhat the management of the stack;
RPN mode is
inspired but
not equivalent to the stack mechanics implemented in most of the calculators produced by HP during its history. Its distinctive feature is the limited number of stack levels (just 4) and the
stack drop;
Extended RPN mode is an extension of regular RPN mode, the only difference is the number of stack levels: 8 levels instead of 4.
The current stack mode is controlled by flags -28 and -29.