ANALOG KEYBOARD

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SGS-THOMSON GRAFING

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APPLICATION NOTE 431

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ST6

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Use of ADC inputs for multiple key decoding

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With the inbuilt A/D converter of any ST6 it is easy to

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implement a small routine which enables ONE port pin, con-

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figured as an ADC input, to decode up to ten different switches*

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All that is necessary is to set one port pin as an ADC input

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Then the program runs in an endless loop until one of the

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connected keys is pushed.

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The value from the ADC data register is then used to decide

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how the program will continue,on reaction to the key-push.

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;***REGISTERS***

ddrpb

.def

0c5h

;port B data direction register

orpb

.def

0cdh

;port B option register

drpb

.def

0c1h

;port B data register

adr

.def

0d0h

;A/D data register

adcr

.def

0d1h

;A/D control register

a

.def

0ffh

;accumulator

;***CONSTANTS***

inpall

.equ

000h

;used for setting all pins input

peg1_2

.equ

00ch

;border to distinguish between switch1 and switch2

peg2_3

.equ

025h

;border to distinguish between switch2 and switch3

peg3_4

.equ

03eh

;border to distinguish between switch3 and switch4

peg4_5

.equ

058h

;border to distinguish between switch4 and switch5

peg5_6

.equ

072h

;border to distinguish between switch5 and switch6

peg6_7

.equ

08ch

;border to distinguish between switch6 and switch7

peg7_8

.equ

0a5h

;border to distinguish between switch7 and switch8

peg8_9

.equ

0beh

;border to distinguish between switch8 and switch9

APPENDIX A: Key Input by Polling