di2483.txt
;************************************************************************************************
; LISTING 1--MULTIPLEXING DIP SWITCHES TO SINGLE I/O PORT
;
; "uC multiplexes DIP switches to I/O port," EDN, Feb 17, 2000, pg 150
; http://www.ednmag.com/ednmag/reg/2000/02172000/designideas.htm#04di3
;***********************************************************************************************

;Microcontroller Multiplexes Multiple DIP Switches to Single I/O Port
;Author: Gregg Willson, ACS Defense, Inc.
;Define constants
	list	p=16c63
#include	"c:\mpasm\P16C63.inc"
;Define RAM storage locations for DIP switch values
TMP0	equ	h'20'	
TMP1	equ	h'21'
TMP2	equ	h'22'
TMP3	equ	h'23'
;Main Routine
Read_32_DIP_Switches
	call	Initialize_Ports	;Setup ports for multiplexing
	movlw	b'11111110'	;Get ready to make port A, bit 0 an output
	call	Read_DIP_Sw	;Read the first DIP switch
	movwf	TMP0		;Save in temporary register
	movlw	b'11111101'	;Get ready to make port A, bit 1 an output
	call	Read_DIP_Sw	;Read the second DIP switch
	movwf	TMP1		;Save it
	movlw	b'11111011'	;Get ready to make port A, bit 2 an output
	call	Read_DIP_Sw	;Read the third DIP switch
	movwf	TMP2		;Save it
	movlw	b'11110111'	;Get ready to make port A, bit 3 an output
	call	Read_DIP_Sw	;Read the fourth DIP switch
	movwf	TMP3		;Save it
	return
; DONE
;Subroutines
Initialize_Ports
	bcf	STATUS, RP0	;Select register Bank 0
	movlw	b'00000000'	;Default port A outputs to 0 to ground switches
	movwf	PORTA
	bsf	STATUS, RP0	;Select register Bank 1
	movlw	b'11111111'	;Make port B all inputs
	movwf	TRISB
	movwf	TRISA		;Make port A all inputs initially
	bcf	OPTION_REG, 7	;Option: Enable weak internal pullups on port B
	return
Read_DIP_Sw
;Enable DIP Switch based on W register value
	bsf	STATUS, RP0	;Select register Bank 1
	movwf	TRISA		;DIP switch is now selected
;Read the data
	bcf	STATUS, RP0	;Select register Bank 0
	movf	PORTB, W	;Put switch values in W register
	return
	END