#include	"E:\MPLAB\p16c711.INC"
	__CONFIG	0x3FF2

;Registers for the NCO DAC
DAC	equ	0x0C	;Holding reg. for DAC value
PACC	equ	0x0D	;Phase Accumulator

;Registers for the sinewave generation
LUPCNT	equ	0x0E	;Loop cntr for sin updates
INDEX	equ	0x0F	;Index into the lookup table

;Reset Vector:
	org	0
	goto	START

;SINE Lookup Table, one cycle, 16 values
	org	0x10
SINTBL	addwf	PCL,f
	retlw	d'128'
	retlw	d'177'
	retlw	d'219'
	retlw	d'246'
	retlw	d'255'
	retlw	d'246'
	retlw	d'219'
	retlw	d'177'
	retlw	d'128'
	retlw	d'79'
	retlw	d'37'
	retlw	d'10'
	retlw	d'1'
	retlw	d'10'
	retlw	d'37'
	retlw	d'79'

;Initialize ports and registers
	;Initialize WDT, DDRs, Regs
START	bsf	STATUS,RP0	;Page 1
	movlw	0x08		;Presc-WDT, 1:1
	movwf	0x81		;Setup WDT & TMR0

	;Setup Ports A&B
	movlw	3		;RA0,1 are Ins
	movwf	TRISA		;RA2,3,4 are Outs

	;Setup ADCON1
	movlw	3		;Make PORTA
	movwf	ADCON1		; Dig I/O
	bcf	STATUS,RP0	;Page 0

	clrf	PACC		;Clear phase accumulator
	clrf	LUPCNT		;Clear the loop counter
	movlw	0x80		;Start the output
	movwf	DAC		; at midscale

;Main loop

MAIN	incf	LUPCNT,f		;1 more pass thru
	btfsc	LUPCNT,5		;When 32 cnts have elapsed,
	call	GETSIN		; get the next value

	call	NCO		;Update the output
	goto	MAIN

;Subroutine that gets the sine value from lookup.  Loop counter
; gets reset.  INDEX increments to point to the next DAC value.
	;Restart counter, update INDEX
GETSIN	clrf	LUPCNT
	incf	INDEX,f
	btfsc	INDEX,4
	clrf	INDEX

	;Get the Sine value from lookup table.
	movf	INDEX,w		;Pass INDEX in 'w' to
	call	SINTBL		; the lookup table
	movwf	DAC		;Save returned value in DAC
	return

;Subroutine that updates the phase accumulator and sends the
; carry bit to PORTA bit 2.
NCO	movf	DAC,w		;Get DAC value
	addwf	PACC,f		;Add it to the phase accum.
	movlw	b'00000'		;Reset bit 2
	btfsc	STATUS,C		;If C = 1,
	movlw	b'00100'		; Set bit 2
	movwf	PORTA		;Send it to PORTA
	return

	END
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