;wave1.asm

;Prototype of an arbitrary waveform generator

;Program memory is used to store the waveform table



;The program can be optimized by locating the waveform

;table in the interna; SRAM, accessing which takes only

;2 clock cycles (instead of 3 for program memory)

;SRAM is accessed with pointer auto increment feature

;that cuts the number of clock cycles taken in 1 loop

;by 1 clock cycle. The final optimized minimum state

;time would be 6 clock cycles instead of current 8



;Dhananjay V. Gadre

;June 10, 1999



;register contains the size of the wave table

.def table_size=r20





.include "8515def.inc"



.cseg

.org 0

        rjmp    RESET           ;Reset Handle

        rjmp    RESET

        rjmp    RESET

        rjmp    RESET

	

RESET: 



       ldi r16, $A0          ;Init the Stack Pointer

       out SPL, r16

       ldi r16, $0

       OUT SPH, r16



       ldi r16, 255          ;configure PORT B for all outputs

       out DDRB, r16       



more:  ldi table_size, 12    ;number of entries in the clock table



                             ;init pointer to the waveform table

                             ;table configured in Program Memory



  	ldi	ZH,high(WAVE_TABLE*2)

	ldi	ZL,low(WAVE_TABLE*2);init Z-pointer





loop_here:       

                       ;Clock Cycles

       lpm             ;3          

                       ;load from program memory



       out PORTB, r0   ;1

                       ;output to the port



       add ZL, r18     ;1

                       ;increment pointer to the table



       dec table_size  ;1

                       ;decrement count



       brne loop_here  ;2

                       ;loop



                       ;Total=8 clock cycles

       rjmp more       



;An arbitrary waveform table        

WAVE_TABLE:

             .db $A0, $A1

             .db $B3, $B2

             .db $32, $33

             .db $35, $75

             .db $f7, $95

             .db $A7, $Af