Programmable calculator including magnetic reading and recording means

Abstract

A modular read-write and read-only memory unit capable of employing both direct and indirect decimal and symbolic addressing, a central processing unit capable of performing both serial binary and parallel binary-coded-decimal direct and indirect memory register arithmetic, and an input-output control unit capable of bidirectionally transferring information between the central processing unit and a number of input and output units are controlled by a microprocessor included in the central processing unit. The input and output units include a keyboard input unit, a magnetic card reading and recording unit capable of bidirectionally transferring information between an external magnetic card and the read-write memory unit, and a solid state output display unit capable of displaying three lines of numeric information. The memory, central processing, input-output control, input, and output units are employed to provide an adaptable programmable calculator that may be operated manually by the user from the keyboard input unit or automatically by a program stored in the read-write memory unit. The calculator may also be employed to load programs into the read-write memory unit from the keyboard input unit, to separately transfer either data or programs bidirectionally between the read-write memory unit and an external magnetic card, and to code programs stored in the read-write memory unit as being secure when they are transferred to an external magnetic card, thereby preventing users of the calculator from re-transferring them to an external magnetic card or obtaining any indication of the individual program steps once they are reloaded into the calculator.