Browse Prior Art Database

USE OF AN A-D CONVERTER IN A MICROCONTROLLER FOR KEY DECODING

IP.com Disclosure Number: IPCOM000007036D
Original Publication Date: 1993-Oct-01
Included in the Prior Art Database: 2002-Feb-20
Document File: 2 page(s) / 89K

Publishing Venue

Motorola

Related People

Michael Rotzer: AUTHOR [+2]

Abstract

This invention is generally applicable to any arrangement having a keypad and a microcontroller containing a A-D converter.

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INC. Technical Developments Voiume 20 October 1993

USE OF AN A-D CONVERTER IN A MICROCONTROLLER FOR KEY DECODING

by Michael Riitzer and Uwe Hennings

  This invention is generally applicable to any arrangement having a keypad and a microcontroller containing a A-D converter.

  In a typical prior art circuit comprising a keypad, such as a hexadecimal keypad, a microprocessor, cou- pled to the keypad, will sequentially pole a number of outputs from the keypad matrix while strobing a plurality ofinputs to the matrix to determine which key in the matrix has been depressed. As will be appreciated, this configuration requires the use of several digital inputs and outputs to and from the microprocessor. Clearly, in a complex circuit where such inputs and outputs are valuable, this is an unde- sirable requirement.

  With reference to the accompanying figure, the requirement to utilize digital inputs on a micro- processor is eliminated if the keypad matrix illus- trated is coupled to a microcontroller having an A-D converter. The keypad illustrated in the figure shows a hexadecimal key pad arrangement, although it will be appreciated that the invention is not limited to a key pad comprising 16 keys. A supply line 10 is cou- pled through a number of varying resistive paths Rl, R2, R3, R4 to a matrix of switches arranged at intersections with a number ofvarying resistive out- puts R5, R6, R7, R8. The resistive outputs R5-R8 are coupled to common circuit node 12 which pro- vides a data signal 14. The data signal is coupled to an A-D converter in a microcontroller. Furthermore, the circuit node 12 is coupled through a further resis- tor to ground.

  The closu...