ANALOG KEYBOARD

11/15

en_kint:

ldi

ddrpb,inpall

;sets all port B pins low — all input

ldi

orpb,02h

;option register:

; sets bit b1 high, the rest low

ldi

drpb,01h

;data register:

; sets bit b0 high, the rest low

;— pb0 becomes input, no pull-up, no int

;

pb1 becomes input with pull-up and int.

;

pb2-7 become input with pull-up, but

;

are not used here

ldi

ior,10h

;interrupt option register:

;— set D4: enable all interrupts

;

reset D5: falling edge on int.input(#2)

ret

;return to the calling address

;*** hd_kint (handle key interrupt) interrupt service routine

;*** evaluates the data resulting in pushing a key.

;*** Interrupt vector #2 (0ff4h and 0ff5h) must point (jump) to hd_kint.

hd_kint:

ldi

drpb,03h

;data register:

; 0000 0011

ldi

ddrpb,01h

;data direction register:

; 0000 0001

; — pb0 becomes output

ldi

orpb,03h

;option register:

; 0000 0011

; — pb0: push-pull output

; — pb1: ADC-input

;

pb2-7 become input with pull-up, but

;

are not used here

ldi

adcr,30h

;A/D control register:

; 0011 0000 — -activate A/D converter

;

-start conversion

;

-disable A/D interrupt

loop:

jrr

6,adcr,loop

;waits until the End Of Conversion

; bit is set (indicator that a conversion

; has been completed)

ld

a,adr

;load acc with the result of the A/D

; conversion

;now the result is compared with the

; values which represent the different

; switches