AT83SND1CXXX-ROTIL datasheet(178/212 Pages) ATMEL

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178

4109J–8051–10/06

AT8xC51SND1C

21. Keyboard Interface

The AT8xC51SND1C implement a keyboard interface allowing the connection of a 4 x n matrix

keyboard. It is based on 4 inputs with programmable interrupt capability on both high or low

level. These inputs are available as alternate function of P1.3:0 and allow exit from idle and

power down modes.

21.1

Description

The keyboard interfaces with the C51 core through 2 special function registers: KBCON, the

keyboard control register (see Table 141); and KBSTA, the keyboard control and status register

(see Table 142).

The keyboard inputs are considered as 4 independent interrupt sources sharing the same inter-

rupt vector. An interrupt enable bit (EKB in IEN1 register) allows global enable or disable of the

keyboard interrupt (see Figure 21-1). As detailed in Figure 21-2 each keyboard input has the

capability to detect a programmable level according to KINL3:0 bit value in KBCON register.

Level detection is then reported in interrupt flags KINF3:0 in KBSTA register.

A keyboard interrupt is requested each time one of the four flags is set, i.e. the input level

matches the programmed one. Each of these four flags can be masked by software using

KINM3:0 bits in KBCON register and is cleared by reading KBSTA register.

This structure allows keyboard arrangement from 1 by n to 4 by n matrix and allow usage of KIN

inputs for any other purposes.

Figure 21-1. Keyboard Interface Block Diagram

Figure 21-2. Keyboard Input Circuitry

21.1.1

Power Reduction Mode

KIN3:0 inputs allow exit from idle and power-down modes as detailed in section “Power Man-

agement”, page 47. To enable this feature, KPDE bit in KBSTA register must be set to logic 1.

Due to the asynchronous keypad detection in power down mode (all clocks are stopped), exit

may happen on parasitic key press. In this case, no key is detected and software must enter

power down again.

21.2

Registers

Table 141. KBCON Register

KIN0

Keyboard Interface

Interrupt Request

EKB

IEN1.4

Input Circuitry

KIN1

Input Circuitry

KIN2

Input Circuitry

KIN3

Input Circuitry

KIN3:0

KINM3:0

KBCON.3:0

KINF3:0

KBSTA.3:0

KINL3:0

KBCON.7:4

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