Browse Prior Art Database

INTERRUPT DRIVEN 4 BY 4 KEYPAD

IP.com Disclosure Number: IPCOM000005778D
Original Publication Date: 1989-Aug-01
Included in the Prior Art Database: 2001-Nov-06
Document File: 3 page(s) / 114K

Publishing Venue

Motorola

Related People

Frederick Cheah: AUTHOR [+3]

Abstract

The design of a4 by 4 keypad can be approached by either adopting the serial or the parallel concept. The serial concept is tedious in terms of software effort, complex in circuitry and slow in response. However, it re- quires few interface lines. The parallel concept on the other hand is less complex in circuitry, IesS SoftWare intensive and faster in response The parallel concept also requires more interface lines, namely, 8 plus an interrupt line for a 4 by 4 keypad.

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6% MOlVROLA Technical Developments Volume 9 August 1989

INTERRUPT DRIVEN 4 BY 4 KEYPAD

by Frederick Cheah, Teh Do Hui & Boh Kai Chek

   The design of a4 by 4 keypad can be approached by either adopting the serial or the parallel concept. The serial concept is tedious in terms of software effort, complex in circuitry and slow in response. However, it re- quires few interface lines. The parallel concept on the other hand is less complex in circuitry, IesS SoftWare

intensive and faster in response The parallel concept also requires more interface lines, namely, 8 plus an interrupt line for a 4 by 4 keypad.

   This article describes a design based on the combination of the two concepts. The design requires less interface lines than the parallel keypad and is superior to the serial concept in terms of response time, circuit complexity and software effort.

   Figure 1 shows the schematic diagram of the 4 by 4 keypad design. This design makes use of an interrupt line to start the key identification process. With the use of the interrupt line, the processor can be in the wait state when it is idling in order to save power. The operation of the circuit is best explained with a flowchart showing the key significant process. (See Figure 2)

   When a key is pressed, say "5': an interrupt is generated to start the execution of the interrupt service routine. The KRES line is first set 'high' to turn off transistor Ql. A counter, COUNT is designated to count the row number of the key pressed. KCLK is pulsed high to set QO of Ul to high. If none of the column bits are set, the KCLK line is pulsed to set Ql to high. COUNT is then incremented by 1 to indicate row 2. This is repeated until a key press is detected. Since "5" is t...