AT89C5131A-RDTIM datasheet(86/184 Pages) ATMEL

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AT89C5130A/31A-M

4337C–USB–02/05

Keyboard Interface

Introduction

The AT89C5130A/31A-M implements a keyboard interface allowing the connection of a

8 x n matrix keyboard. It is based on 8 inputs with programmable interrupt capability on

both high or low level. These inputs are available as an alternate function of P1 and

allow to exit from idle and power down modes.

Description

The keyboard interface communicates with the C51 core through 3 special function reg-

isters: KBLS, the Keyboard Level Selection register (Table 72), KBE, The Keyboard

interrupt Enable register (Table 71), and KBF, the Keyboard Flag register (Table 70).

Interrupt

The keyboard inputs are considered as 8 independent interrupt sources sharing the

same interrupt vector. An interrupt enable bit (KBD in IE1) allows global enable or dis-

able of the keyboard interrupt (see Figure 37). As detailed in Figure 38 each keyboard

input has the capability to detect a programmable level according to KBLS.x bit value.

Level detection is then reported in interrupt flags KBF.x that can be masked by software

using KBE.x bits.

This structure allow keyboard arrangement from 1 by n to 8 by n matrix and allow usage

of P1 inputs for other purpose.

Figure 37. Keyboard Interface Block Diagram

Figure 38. Keyboard Input Circuitry

P1.0

Keyboard Interface

Interrupt Request

KBD

IE1.0

Input Circuitry

P1.1

Input Circuitry

P1.2

Input Circuitry

P1.3

Input Circuitry

P1.4

Input Circuitry

P1.5

Input Circuitry

P1.6

Input Circuitry

P1.7

Input Circuitry

KBDIT

P1:x

KBE.x

KBF.x

KBLS.x

Vcc

Internal Pull-up

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