Telephone with digit cancellation

An improvement in telephone equipment which enables a user to cancel the wrong digit of a misdialed number regardless of its position in the number without cancelling other digits in the number.

This is an invention in the telephone art. More particularly, it relates to 
apparatus which enables the correction of a misdialed number without the 
need to redial the entire number. 
It is common for users of telephones to dial directly without the 
assistance of an operator. In the United States in direct dialing long 
distance numbers it is generally necessary to dial at least ten digits to 
make connection with a desired location. If a wrong digit is dialed it is 
necessary to begin all over again and redial the entire number. 
It is an object of this invention to make it easier to use a telephone. 
One of the advantages of the invention is that it enables a user of a 
telephone to correct a misdialed digit of a number without redialing the 
entire number regardless of the position of the digit in the number. 
One of the features of the invention is the provision of a cancellation 
button on a telephone to enable the cancellation of a digit in a dialed 
number. 
In accordance with the invention there is provided an improvement in a 
telephone system in which connections are made between telephone 
instruments located at different locatios. Each instrument is assigned a 
unique number including a plurality of digits. The system includes input 
means associated with each instrument and operable by a user to generate a 
separate signal for each of the digits. In order to make connection 
between two instruments a user of one instrument generates in series each 
of the signals associated with the digits assigned to the second of the 
instruments. The improvement comprises cancellation means associated with 
each of prescribed ones of said instruments and operable by a user during 
the serial generation of a plurality of signals to cancel a predetermined 
one of said signals regardless of its position in the series.

A push button telephone instrument incorporating storage registers and 
control circuitry which enables a completed telephone number to be stored 
and subsequently transmitted after all the push buttons associated with a 
telephone number have been operated in the appropriate sequence is known 
per se. The digits of the telephone number are stored in binary code in 
storage registers. For transmission, the binary codes are translated into 
the appropriate form--typically in the form of dial-type impulses--and 
transmitted automatically together with the appropriate interdigit pauses 
between the train of pulses. As known, alternative coded forms such as 
binary codes, frequency codes, etc. may be used for transmitting the 
number to the exchange. In this way, all the advantages of rapid push 
button telephone operation may be gained on existing telephone exchanges 
without the necessity for modifying or adding to the existing equipment at 
the telephone exchange. In the embodiment described herein, the function 
and operation are explained in relation to the above-mentioned push button 
telephone instrument for the purposes of simplicity and clarity, but it 
will be apparent to any person skilled in the art that if any changes are 
needed in the equipment as shown to enable it to function in combination 
with any other telephone instrument incorporating digit storage and 
transmission means then such changes will be of an obvious nature. 
Referring now to FIG. 1 of the drawing, there is shown a typical keyboard 
11 with twelve push buttons identified as 0, 1 through 9, T and C. Each of 
these buttons is connected to microprocessor 13 which operates with its 
associated memory 15. Microprocessor 13 is also connected to display 17 
and through an appropriate telephone line 19 to the telephone exchange. 
The capacity of microprocessor 13 and memory 15 depends upon the number of 
digits it is desired to store which, in turn, typically would depend on 
the maximum number of digits in the telephone numbers to be dialed. It is 
presently considered that a 16-digit number would be sufficient for most 
applications. A 4-bit microprocessor with appropriate first-in, first-out 
registers is sufficient to handle 16-digit numbers. 
The buttons on keyboard 11 are provided to input the digits 0, and 1 
through 9 of any telephone number. Button C is connected to an 
input/output port of microprocessor 13 in order to effect the cancellation 
of the last number stored in memory 15. Transmission button T is connected 
to another input/output port of microprocessor 13 in order to cause the 
microprocessor to output a stored telephone number in the appropriate 
format with appropriate interdigit pauses to the telephone exchange. 
Display 17 is utilized to display in a format readable from left to right 
the numbers in memory 15 corresponding to the telephone number being keyed 
in through keyboard 11. Any common display device would be suitable, 
although a liquid crystal display such as that utilized by many well known 
types of pocket calculators is preferred. In a preferred embodiment of the 
invention, keyboard 11, microprocessor 13, memory 15, and display 17 are 
all integral parts of the same telephone instrument. 
In FIG. 2 it can be seen that when the hookswitch of a telephone instrument 
adapted to practice the invention is operated, keyboard 11 is activated. 
Operation of any of the buttons 0 and 1 through 9 causes the signals 
corresponding to the associated digits to be stored in a first-in, 
first-out register comprising memory 15. As long as transmission key or 
button T is not operated, the storage of signals corresponding to inputted 
numbers is continuously enabled. While cancellation key or button C is 
unoperated, the display is enabled and the number being dialed can be read 
out from the display. If cancellation key C is operated, it causes the 
removal of the last entered digit from memory 15. This causes a change in 
the display so that it thereafter displays only those numbers dialed prior 
to the cancelled or removed number. The operation of button C also 
prevents transmission to the exchange notwithstanding transmission key T 
may be operated. Otherwise, when transmission key T is operated, a dialed 
and stored number is transmitted to the exchange. 
In operation, a user of keyboard 11 would input a desired telephone number 
in the usual manner. Should this be done correctly, he pushes the 
transmission key T at the end of dialing and the number dialed is 
transmitted to the exchange by microprocessor 13. If in the course of 
dialing an incorrect digit is entered, the user presses cancellation key C 
immediately after such entry. This causes microprocessor 13 to remove the 
last entered digit from the first-in, first-out register of memory 15. 
This causes the display to discontinue displaying this digit. The user 
could then enter the correct digit and continue dialing to completion. 
While a display is shown in the preferred embodiment, this is for 
convenience only. It is to be understood that such a display is not 
necessary and that the advantages of the invention could be enjoyed 
notwithstanding a display is not provided. 
It should be apparent that various modifications of the above will be 
evident to those skilled in the art and that the arrangement described 
herein is for illustrative purposes and is not to be considered 
restrictive.