AN431 datasheet(8/15 Pages) STMICROELECTRONICS

8 / 15 page

ANALOG KEYBOARD

8/15

peg9_10

.equ

0d9h

;border to distinguish between switch9 and switch10

ldi

ddrpb,inpall

;sets all port B pins low — all input

ldi

orpb,01h

;option register:

;sets bit b0 high, the rest low

ldi

drpb,01h

;direction register:

;sets bit b0 high, the rest low

;— pb0 becomes analog input

;

pb1-7 become input with pull-up, but

;

are not used here (only one pin may be

;

analog input for A/D at the same time)

ldi

adcr,30h

;A/D control register:

; 0011 0000 — -activate A/D converter

;

-start conversion

;

-disable A/D interrupt

loop:

jrr

6,adcr,loop

;loop until the End Of Conversion bit is

;set (indicator that a conversion has

;been completed)

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

sw1:

cpi

a,peg1_2

;compare with peg1_2

jrnz

sw2

;A/D result was smaller than peg1_2

; — switch1 was pressed: jump to s1

sw2:

cpi

a,peg2_3

;compare with peg2_3

jrnz

sw3

;A/D result was smaller than peg2_3

; — switch2 was pressed: jump to s2

sw3:

cpi

a,peg3_4

;compare with peg3_4

jrnz

sw4

;A/D result was smaller than peg3_4

; — switch3 was pressed: jump to s3

sw4:

cpi

a,peg4_5

;compare with peg4_5

jrnz

sw5

;A/D result was smaller than peg4_5

; — switch4 was pressed: jump to s4

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