Patent US 4,145,752

An adaptable programmable calculator is provided by employing a modular read-write and read-only memory unit 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 capable of performing both serial binary and parallel binary-coded-decimal arithmetic, 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, such as a keyboard and an output display unit. The memory, central processor, and input-output control units are controlled by a microprocessor included in the central processing unit. Functions and subroutines that are defined by the user, stored in the calculator memory, and associated with definable keys of the keyboard are each automatically assigned a sequence of line numbers that is independent of the sequence of line numbers assigned to any other function, subroutine, or mainline program stored in the calculator memory. Such defined functions and subroutines defined by the user and stored in the calculator memory may be selectively erased from memory without thereby altering a mainline program or other functions or subroutines stored therein.