AT89C51ED2-RDTIM datasheet(60/137 Pages) ATMEL

60 / 137 page

AT89C51RD2/ED2

4235E–8051–04/04

Keyboard Interface

The AT89C51RD2/ED2 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 alternate function of P1 and allow to

exit from idle and power-down modes.

The keyboard interfaces with the C51 core through 3 special function registers: KBLS,

the Keyboard Level Selection register (Table 45), KBE, the Keyboard interrupt Enable

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 27). As detailed in Figure 28 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 allows

usage of P1 inputs for other purpose.

Figure 27. Keyboard Interface Block Diagram

Figure 28. Keyboard Input Circuitry

Power Reduction Mode

P1 inputs allow exit from idle and power-down modes as detailed in Section “Power

Management”, page 82.

P1:x

KBE.x

KBF.x

KBLS.x

Vcc

Internal Pullup

P1.0

Keyboard Interface

Interrupt Request

KBD

IE1

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

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