AT89C51ED2-RDTUM datasheet(59/137 Pages) ATMEL

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4235K–8051–05/08

AT89C51RD2/ED2

15. 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 Key-

board Level Selection register (Table 15-3), KBE, the Keyboard interrupt Enable register

(Table 15-2), and KBF, the Keyboard Flag register (Table 15-1).

15.0.1

Interrupt

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

rupt vector. An interrupt enable bit (KBD in IE1) allows global enable or disable of the keyboard

interrupt (see Figure 15-1). As detailed in Figure 15-2 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 15-1. Keyboard Interface Block Diagram

Figure 15-2. Keyboard Input Circuitry

15.0.2

Power Reduction Mode

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

ment”, page 80.

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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