Programmable calculator including boolean flag variable means

Abstract

An adaptable programmable calculator is provided by employing modular read-write and read-only memory units capable of being expanded to provide the calculator with additional program and data storage functions oriented towards the environment of the user, a central processing unit, and an input-output control unit capable of bidirectionally transferring information between the memory or central processing units and a number of input and output units. The memory, central processor, and input-output control units are controlled by a microprocessor included in the central processing unit. The input and output units include a keyboard input unit with a plurality of sections capable of being defined by plug-in read-only memory modules and stored programs added by the user, a magnetic card reading and recording unit capable of bidirectionally transferring information between an external magnetic card and the calculator, an output display unit capable of displaying every alphabetic and numeric character and many other symbols individually and in a line of one or more alphameric statements, and a printer unit capable of printing on thermally sensitive paper every alphabetic and numeric character and many other symbols individually and in alphameric statements or messages. The calculator includes a multiplicity of programmable boolean flag variables that may be designated from the keyboard input means and employed as part of an alphameric statement. Selected ones of the boolean flag variables may be manually set from the keyboard at any time during execution of a program stored in the read-write memory. A dedicated one of the boolean flag variables is automatically set by the calculator when a mathematically incorrect program statement or an arithmetic underflow or overflow is encountered during program execution.