METHOD AND CIRCUIT FOR CAPTURING KEYPAD DATA SERIALIZING/DESERIALIZING AND REGENERATING THE KEYPAD INTERFACE

• US 20090106462A1
• Filed: 04/30/2008
• Published: 04/23/2009
• Est. Priority Date: 05/03/2007
• Status: Active Grant

• Current Assignee: Semiconductor Components Industries LLC (ON Semiconductor Corporation)
• Original Assignee: Fairchild Semiconductor Corporation (ON Semiconductor Corporation)
• Inventors: Freitas, Oscar, Boomer, James
• Granted Patent: US 8,321,598 B2
• Time in Patent Office: Days
• US Class Current: 710/30
• CPC Class Codes: H03M 11/20 Dynamic coding, i.e. by key scanning H03M11/26 takes precedence

Abstract

A serializer/deserializer interfacing a keypad or keyboard to a processing system is illustrated. In one application, the processor is arranged to generate keypad scan and input keypad sense lines directly. However, to minimize wires on intervening cables, a serializer and deserializer is inserted between the processor system, the serializer/deserializer forming a virtual keypad. In this case, the processor scans the deserializer as if it were the keypad and the keypad is scanned by the serializer as if it were the processor. However, the serializer converts the scanning of the keypad into a serial bit stream that is sent to the deserializer using only a data line and a clock line. The deserializer accepts the serial bit stream and reconfigures the data into a response that mimics the response of the physical keypad as the computer system scans the virtual keypad, the deserializer. In one embodiment an actual second keypad is formed in the deserializer and activated as the first keypad is activated, wherein the computer scans the second keypad in the usual fashion.

Claims

1. A system for scanning a first keypad or keyboard, the system comprising:

a computer system arranged to generate first scan line signals to and receive first sense line signals as if the computer system was attached to the keypad;

a deserializer having an interface that receives the first scan line signals from the computer system and generates the first sense line signals to the computer system, wherein the deserializer mimics the response that a keypad would when attached to the computer system'"'"'s scan and sense lines;

a serializer that generates second scan line signals to and receives second sense line signals from a keypad;

wherein the serializer mimics scan and sense line signals of the computer system, wherein the scan and sense lines signals are formatted into a serial bit stream by the serializer;

a connection between the deserializer and the serializer, the serial connection arranged to send data in a serial fashion;

wherein the serializer sends the bit stream over the connection, wherein the bit stream is received by the deserializer and reformatted into a form that is returned to the computer system as if the keypad was attached to the computer system.

2. The system of claim 1 further comprising a circuit that detects when any key on the keypad was depressed.

3. The system of claim 1, wherein the connection between the serializer and the deserializer comprises a clock signal and the serial data bit stream.

4. The system of claim 1 further comprising a second switch matrix in the deserializer with scan and sense lines that duplicate the scan and sense lines of the first keypad or keyboard, wherein the deserializer activates a key in the second keypad that corresponds in row and column locations as was the key activated in the first keypad.

5. The system of claim 1 wherein the first keypad of keyboard comprises CMOS transistor switches wherein when the key may be activated by a high or a low signal and the output may be a low or high signal, respectively.

6. The system of claim 1 wherein the first keypad or keyboard comprises NMOS or PMOS switches.

7. The system of claim 1 further comprising a blocking diode in series with each key, wherein the blocking diode suppresses ghosting.

8. A process for scanning a first keypad or keyboard, the process comprising the steps of:

sending first scan line signals to and receiving first sense line signals from a computer system as if the first scan and sense signals were sent to and received from the keypad;

mimicking, by a deserializer, a keypad receiving the first scan line signals and generating the first sense line signals,

generating second scan line signals to and receiving second sense line signals from the keypad;

formatting the second scan and sense line signals into a serial bit stream;

transferring the serial bit stream to the deserializer;

receiving the serial bit stream by the deserializer;

reformatting the receiving serial bit stream into a form that is returned to the computer system as if the keypad was attached to the computer system.

9. The process of claim 8 further comprising the step of detecting when any key on the keypad was depressed.

10. The process of claim 8, wherein the step of transferring comprises the steps of sending a clock signal suitable for loading a serial data bit.

11. The process of claim 8 wherein the step of reformatting the received serial bit stream comprises the steps of:

determining which key in the first keypad was depressed, and

activating a second keypad, wherein the second keypad duplicated the first keypad with respect to rows and columns, and wherein the key activated in the second keypad that corresponded in row and column as was the key activated in the first keypad.

12. The process of claim 8 further comprising the step of suppressing or blocking ghost signals by inserting a diode in series with each key switch.