T89C51RC2-3CSIM datasheet(59/117 Pages) ATMEL

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T89C51RB2/RC2

4105D–8051–10/06

Keyboard Interface

The T89C51RB2/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 interface interfaces with the C51 core through 3 special function registers:

KBLS, the Keyboard Level Selection register (Table 44), KBE, The Keyboard interrupt

Enable register (Table 43), and KBF, the Keyboard Flag register (Table 42).

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 22). As detailed in Figure 23 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 22. Keyboard Interface Block Diagram

Figure 23. Keyboard Input Circuitry

Power Reduction Mode

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

down Mode”, page 76.

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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