by Bob Axtell of
http://www.platinumtechnical.com
;********************************************************; ; Code snippet for reading 7 switches on a single PIN ; Routine assumes that ADCON0 and ADCON1 are set to ; appropriate values for the PIC used. ; The routine tests 8bit ADC value against the voltage ; level presented. If it is LOWER than the test then ; that switch is grounded. NOTE: This can be minimized ; further. NOTE: this should be executed during an ; interrupt to make sure that the snippet is not missed. ;********************************************************; ;process keyboard: inside ints only keybd: clrf status rrf adresh,w movwf tmp1_ bank1 rrf adresl,w clrf status movwf tmp_ rrf tmp1_,f rrf tmp_,f ;now fixed to 8 bits, NOT 10 bits clrf tmp1_ ;used to locate switch number incf tmp1_,f ;=SW1 movlw -d'18' ; 0.0V + 0.7V/2 = 0.35V Test limit addwf tmp_,w ;OK Pressed? btfss status,c ;check if LESS goto keybd0 ;jump if OK SW pressed incf tmp1_,f movlw -d'54' ; 0.7V + 0.35V = 1.05V addwf tmp_,w ;DN Pressed? btfss status,c ;check if LESS goto keybd0 ;jump if DN SW pressed incf tmp1_,f movlw -d'90' ; 1.4v + 0.35V = 1.75V addwf tmp_,w ;<< Pressed? btfss status,c ;check if LESS goto keybd0 ;jump if << SW pressed incf tmp1_,f movlw -d'125' ; 2.1V + 0.35V = 2.45V addwf tmp_,w ;< pressed? btfss status,c ;check if LESS goto keybd0 ;jump if < SW pressed incf tmp1_,f movlw -d'161' ;2.8V + 0.35V = 3.15V addwf tmp_,w ;> pressed? btfss status,c ;check if LESS goto keybd0 ;jump if > SW pressed incf tmp1_,f movlw -d'197' ;3.5V + 0.35V = 3.85V addwf AN0,w ;>> pressed? btfss status,c ;check if LESS goto keybd0 ;jump if >> SW pressed incf tmp1_,f movlw -d'233' ;4.2V + 0.35V = 4.55V addwf AN0,w ;UP pressed? btfsc status,c ;check if LESS ; no switches are pressed, so done goto keybd1 ; now process the switches keybd0: incf tmp1_,w movwf KEY ;value will read 1 to 7 for appropriate SW bsf flags,KYPRESS ;tell system it is time to service keypress keybd1: bsf adcon0,GO ;read for next time return ;********************************************************; ; end of snippet ;********************************************************;
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