AT89C5131A-RDTIL datasheet(85/185 Pages) ATMEL

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AT89C5131A-L

4338E–USB–06/06

Keyboard Interface

Introduction

The AT89C5131A-L 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 70), KBE, The Keyboard

interrupt Enable register (Table 69), and KBF, the Keyboard Flag register (Table 68).

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 39). As detailed in Figure 40 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 39. Keyboard Interface Block Diagram

Figure 40. 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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