AT80SND1C-ROTIL datasheet(179/210 Pages) ATMEL

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179

AT8xC51SND1C

4109E–8051–06/03

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.

Description

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

the keyboard control register (see Table 151); and KBSTA, the keyboard control and

status register (see Table 152).

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

same interrupt vector. An interrupt enable bit (EKB in IEN1 register) allows global

enable or disable of the keyboard interrupt (see Figure 134). As detailed in Figure 135

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 soft-

ware 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 134. Keyboard Interface Block Diagram

Figure 135. Keyboard Input Circuitry

Power Reduction Mode

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

Management”, page 46. 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.

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

AT80SND1C-ROTIL 데이터시트(PDF) 179 Page - ATMEL Corporation

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