Circuit for detecting keypad conditions in a microprocessor controlled telephone instrument

• US 4,598,174 A
• Filed: 11/13/1984
• Issued: 07/01/1986
• Est. Priority Date: 11/13/1984
• Status: Expired due to Fees

• Current Assignee: AG Communication Systems Corp. (Nokia Corporation)
• Original Assignee: GTE Communication Systems Corporation (Verizon Communications Inc.)
• Inventors: Pommer, Karl E. II
• Primary Examiner(s): Dwyer, James L.
• Application Number:
  US06/670,084
• Time in Patent Office: 595 Days
• Field of Search: 179/81 R, 179/84 R, 179/84 VF, 179/84 A, 179/84 L, 179/90 AN, 179/90 B, 179/90 BB, 179/90 BD, 179/90 CS
• US Class Current: 379/354
• CPC Class Codes: H04M 1/26 Devices for calling a subscriber H04M1/66 takes precedence

Abstract

A technique for evaluating keypad conditions while utilizing only a minimum number of ports in a microprocessor involved in control of a telephone instrument. Because of the limited number of ports available and necessity to also evaluate conditions of mode selecting strap switches, the utilization of a reduced number of ports is highly desirable in such an enviroment. Such a reduction becomes an absolute necessity particularly in dealing in those enviroments that include random access memories, read only memories, pulse dialers, integrated circuits and liquid crystal displays. A combination of diode gating, resistive decoupling and time multiplexing techniques are used to match the input/output requirements to the available ports of a specific microprocessor.

Claims

1. A circuit arrangement adapted to maximize the utilization of a microprocessor associated with a telephone comprising:

a microprocessor including a plurality of four pin ports and a serial output port;

the pins of a first port connected as an output to the circuitry of an associated telephone;

said serial output port connected to a shift register;

said shift register further including a plurality of parallel circuit outputs connected to a random access memory;

the pins of a second port connected as inputs to said random access memory;

the pins of a third port also each connected to data in-out connections of said random access memory and each pin of said third port also connected to a DTMF dialer circuit; and

one of said pins of said first port also connected to an enable input of said DTMF dialer circuit.

2. A circuit arrangement as claimed in claim 1 wherein:

there is further included a liquid crystal display and a plurality of circuit connections between said liquid crystal display and said microprocessor.

3. A circuit arrangement as claimed in claim 1 wherein:

there is further included a keypad associated with said telephone including a plurality of column output lines connected to the pins of a fourth port;

said keypad further including a plurality of parallel row output conductors connected to a multiplexer;

said multiplexer including a plurality of outputs connected to the pins of a fifth port; and

a pair of select outputs from said multiplexer connected to two of the pins of said second port;

4. A circuit arrangement as claimed in claim 3 wherein:

there is further included an output from at least one strap switch connected to at least one of the pins of said fourth port and a circuit conductor from at least one of said strap switches connected to one of said pins of said second port.

5. A circuit arrangement as claimed in claim 4 wherein:

said telephone further includes a hookswitch including circuit connections to said fourth port.

6. A circuit arrangement as claimed in claim 4 wherein:

there is further included an inverter circuit included in each column output line connected to the pins of said fourth port.

7. A circuit arrangement as claimed in claim 6 wherein:

each of said column output lines further include a diode serially connected between said inverter and said keypad.

8. A circuit arrangement as claimed in claim 4 wherein:

the output voltage from said strap switch is decoupled by a resistor element to inhibit any effect on output data from said microprocessor to said keypad control lines.