AT89C51RB2-3CSIM datasheet(64/127 Pages) ATMEL

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AT89C51RB2/RC2

4180C–8051–12/03

Keyboard Interface

The AT89C51RB2/RC2 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 53), 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 IEN1) allows global enable or dis-

able of the keyboard interrupt (see Figure 23). As detailed in Figure 24 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 allows keyboard arrangement from 1 by n to 8 by n matrix and allow

usage of P1 inputs for other purpose.

Figure 23. Keyboard Interface Block Diagram

Figure 24. Keyboard Input Circuitry

Power Reduction Mode

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

down Mode”, page 82.

P1:x

KBE. x

KBF. x

KBLS. x

Internal Pull-up

P1.0

Keyboard Interface

Interrupt Request

KBD

IEN1

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

AT89C51RB2-3CSIM Datasheet(PDF) 64 Page - ATMEL Corporation

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