[ASM] Sampling an inputted sine wave

[nemo]

I'm working on this project for school... and here's the assignment:

  Quote

Input shall be a 100 Hz sinewave of amplitude 2 volts peak-to-peak with no offset. You are to take samples at 100 Hz, 200 Hz, and 300 Hz. There shall be 300 samples of each stored in the microprocessor memory. The results shall be sent to and stored in the PC for analysis using an application program.

The microprocessor I'm using is a Motorola M68HC08. The circuit is constructed using a USB->Serial Cable which connects the Tx/Rx of the cpu. Here is the current code (some was given, some wasn't). The idea is to read the Rx at obviously 100hz.. etc... I'm confused as to exactly what needs to be done. I figured: load the sampling rate into memory, decrement the register, get the sample, and loop until it's at 0. I'm just stuck on exactly how this needs to be implemented. Once that is done then I'm using Matlab to read what is outputted and displaying on a graph...

Can I get some help... if you can?

;ASSUMES PTA0 IS TX/RX
DDRA			 EQU	 $04
PTA			  EQU	 $00
;-----SCI PARAMETERS-------------
RXTXPIN		  EQU	 $0	  ;PIN PTA0
DATA_BITS		EQU	 $08
;NOTE- ONLY 1 STOP BIT IMPLEMENTED
;NOTE- PARITY NOT IMPLEMENTED
;---------------------------------
ADCCLK		   EQU	 $3F	 ;DEFINE ADCCLK
ADCSCR		   EQU	 $3C	 ;DEFINE ADCSCR
ADCDATA		  EQU	 $3E	 ;DEFINE ADCDATA

				ORG	  $EE00

start:		  mov	  #$31,$1f;disable COP, set 3V operation

			  ;PLACE your program between the lines
;--------------------------------------------------------------
;		  configure adc... continous conversion on.  3.2mhz clock
				MOV	   #0,ADCCLK	 ;configure ADC clock
				MOV	   #$21,ADCSCR;configure ADC statue control register

wait			bclr	  7,ADCSCR,wait


				lda	   $64
				deca
				bsr	   putstr		;output string
loop:		   bsr	   getbyte	;get a character
				bsr	   putbyte	;output it
				ldhx	  #command	  ;point to command string
				bsr	   putstr		;output it

				bra	   loop		  ;repeat forever
;--------------------------------------------------------------
			  ;putstr(HX)
putstr		  psha			  ;callee save
				pshx
				pshh
nextchr		 lda	 ,x		;get next character from string
				beq	 donestr;if zero, done
				bsr	 putbyte;else output it
				aix	 #1		;point to next char
				bra	 nextchr;repeat
donestr		 pulh			  ;callee restore
				pulx
				pula
				rts


			  ;putbyte(A)
putbyte		 pshx				  ;callee save
				psha
				bset	RXTXPIN,DDRA  ;set to TX
				bclr	RXTXPIN,PTA;output start bit
				bsr	 delbit		;wait 1 bit time
				ldx	 #DATA_BITS	;# data bits
nextb		   lsra				  ;shift next lsb out
				bcc	 zerob		 ;determine to send 0 or 1
oneb			bset	RXTXPIN,PTA;send '1'
				bsr	 delbit		;
				dbnzx   nextb
				bra	 stopb
zerob		   bclr	RXTXPIN,PTA;send '0'
				bsr	 delbit
				dbnzx   nextb
stopb		   bset	RXTXPIN,PTA;send 1 stop bit
				bsr	 delbit
				pula
				pulx
				rts

			  ;DELBIT()
delbit		  pshx						  ;delay approx 1/9600s
				ldx	 #!101
doit			dbnzx   doit
				pulx
				rts

			  ;A=GETBYTE()
getbyte		 bclr	RXTXPIN,DDRA		  ;set to input
gbpollst		brset   RXTXPIN,PTA,gbpollst  ;wait start bit
				bsr	 getbit				;get start bit
				bcs	 gbpollst			  ;check if false start
				lda	 #$80				  ;sentinel to catch done
bitlp		   bsr	 getbit				;get next bit (into C)
				rora						  ;shift it in
				bcc	  bitlp				;continue if not sentinel-done
				bsr	  getbit			;get stop bit
				rts

			  ;C=GETBIT()- uses majority vote algorithm, timed for 1 bit time
getbit		  pshx						  ;get one bit @9600 baud
				psha
				ldx	 #!31
				lda	 #!10
lloop		   brset   RXTXPIN,PTA,next	  ;test line value
next			sbc	 #0
				dbnzx   lloop
				rola
				pula
				pulx
				rts

command:		db	  " is the key you hit... do it again right now!",$0d,$0a,0
prompt:		 db	  "Type a key to begin...",$0d,$0a,0

DUMMYISR		RTI

				ORG	 $FDEB
			  ;interrupt redirect jump table- add a jump to your favority ISR
				JMP	 DUMMYISR	 ;Alternate ADC interrupt vector
				JMP	 DUMMYISR	 ;	'	 KBD wakeup '	'
				JMP	 DUMMYISR	 ;	'	 TOF		'	'
				JMP	 DUMMYISR	 ;	'	 Timer Ch.1 '	'
				JMP	 DUMMYISR	 ;	'	 Timer Ch.0 '	'
				JMP	 DUMMYISR	 ;	'	 IRQ		'	'
				JMP	 START		;	'	 RESET	  '	'