Calculator having merged key codes

DETAILED DESCRIPTION It is an object of this invention to reduce the amount of storage space required in a programmable, electronic calculator by multi-key instructions.
In accordance with the preferred embodiment of the present invention means are provided for generating a single key code, herein called a merged code, for each of several functions requiring a prefix key and a function key to initiate the function.
A portable, programmable, electronic calculator may have, for example, 35 keys on its keyboard.
A unique key code in the form of a binary number is usually assigned to each key and thus a calculator having 35 keys requires a six-digit binary code to uniquely represent each key.
However, six binary digits can represent up to 64 unique combinations and a calculator having only 35 keys thus has 29 spare or unused key codes.
Some or all of these spare key codes can be used to represent those functions that are accessible from the keyboard only by first actuating a prefix key.
When the calculator is being programmed, each key code is entered into the program memory after the corresponding key is depressed.
When a prefix key is depressed, a flag is also set in a status register in the calculator.
If the following key is one that may be both validly prefixed by and merged with the preceding key, the flag in the status register causes the calculator to replace the previously stored prefix key code by a merged key code representing both the prefix and the subsequently depressed key.
The merged key codes thus save program memory space by storing only a single code representative of the desired operation.