DDS (generating sine waves) with onboard DAC using latest PIC 16F chips?

[HankMcSpank]

If there are interrups involved, maybe it is a good idea to disable just before the routine, so R0 and R2 are not messed up.

Ioannis

From my limited understanding...the whole premise of generating waveforms via DDS is to get in & get out the interrupt routine as fast as possible before the next interrupt arrives (else it all fails badly)...in such an instance, I'd say it'd be better to keep the timer interrupt running all the time (since they're be overhead, however small wrt stopping the interrupts)

ok, I slapped the most basic (1 pole) filter with a corner frequency set at about 10khz on the HPWM pin, here's 500Hz...



a bit of noise (could probably do with another filter pole).

Need to have a bit more play

Code to date...

@ __CONFIG _CONFIG1, _FCMEN_OFF & _FOSC_INTOSC & _WDTE_OFF & _MCLRE_OFF & _CP_OFF & _IESO_OFF & _BOREN_OFF & _PWRTE_OFF & _LVP_OFF
@ __CONFIG _CONFIG2, _LVP_OFF
INCLUDE "DT_INTS-14.bas" ' Base Interrupt System
Osccon = %01111010   'sets the internal oscillator to 16Mhz
DEFINE  OSC 16
TrisC.5 = 0     'Pin2 (HPWM) an output     
CM1CON0 = 0   ' COMPARATORS OFF
CM2CON0 = 0   ' COMPARATORS OFF
tuning_word         VAR word
accumulator         VAR WORD
out                 VAR BYTE
'HPWM SETTINGS uses timer 2
CCP1CON  = %00001100     'Turn HPWM on on CCP1
CCPR1L.6 = 0             'only using 8 bit PWM so clear the top two bits 
CCPR1L.7 = 0             'only using 8 bit PWM so clear the top two bits
PR2 = 79                'this PWM frequency of  50khzKHz allows a maximum of 320 values
T2CON = %00000100        'TIMER2 ON 1:1 PRESCALER 1:1 POSTSCALER
 
' setsup an interrupt based on Timer4 overflowing (timer4 will overflow at 20,000 times per second, see further)
ASM
INT_LIST  macro ; IntSource,    Label,         Type, ResetFlag?
    INT_Handler  TMR4_INT,  _DDS,  asm,  YES
    endm
    INT_CREATE       ; Creates the interrupt processor
ENDASM
T4CON.2 = 1     ' Timer4 on
PR4 =  199      ' this should yield an exact 'interrupt rate of 20khz' at 16Mhz.
ACCUMULATOR = 0          ' clear down the accumulator before starting.
@ INT_ENABLE TMR4_INT
TUNING_WORD = 1638 ' this sets the required output frequency (tuning_word value = req_freq/20,000 * 65536)  1638 = 500hz
'CCP1CON.4 = Test.0       'Bit 0
'CCP1CON.5 = Test.1       'Bit 1
'CCPR1L    = Test >> 2    'Bit 2-7
Main:
    pause 1
    goto main
END
'+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
DDS:
'toggle PortA.5
ACCUMULATOR = ACCUMULATOR + tuning_word
' ok, lookup the high byte of the accumulator....
Lookup Accumulator.HighBYTE, [$80,$83,$86,$89,$8C,$8F,$92,$95,$98,$9C,$9F,$A2,$A5,$A8,$AB,$AE,$B0,$B3,$B6,$B9,$BC,$BF,$C1,$C4,_
$C7,$C9,$CC,$CE,$D1,$D3,$D5,$D8,$DA,$DC,$DE,$E0,$E2,$E4,$E6,$E8,$EA,$EC,$ED,$EF,$F0,$F2,$F3,$F5,$F6,$F7,$F8,$F9,$FA,$FB,$FC,$FC, _
$FD,$FE,$FE,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FE,$FE,$FD,$FC,$FC,$FB,$FA,$F9,$F8,$F7,$F6,$F5,$F3,$F2,$F0,$EF,$ED,$EC, _
$EA,$E8,$E6,$E4,$E2,$E0,$DE,$DC,$DA,$D8,$D5,$D3,$D1,$CE,$CC,$C9,$C7,$C4,$C1,$BF,$BC,$B9,$B6,$B3,$B0,$AE,$AB,$A8,$A5,$A2,$9F,$9C, _
$98,$95,$92,$8F,$8C,$89,$86,$83,$7F,$7C,$79,$76,$73,$70,$6D,$6A,$67,$63,$60,$5D,$5A,$57,$54,$51,$4F,$4C,$49,$46,$43,$40,$3E,$3B, _
$38,$36,$33,$31,$2E,$2C,$2A,$27,$25,$23,$21,$1F,$1D,$1B,$19,$17,$15,$13,$12,$10,$0F,$0D,$0C,$0A,$09,$08,$07,$06,$05,$04,$03,$03, _
$02,$01,$01,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$01,$01,$02,$03,$03,$04,$05,$06,$07,$08,$09,$0A,$0C,$0D,$0F,$10,$12,$13, _
$15,$17,$19,$1B,$1D,$1F,$21,$23,$25,$27,$2A,$2C,$2E,$31,$33,$36,$38,$3B,$3E,$40,$43,$46,$49,$4C,$4F,$51,$54,$57,$5A,$5D,$60,$63, _
$67,$6A,$6D,$70,$73,$76,$79,$7C],Out
' now use that 'Out' value to change HPWM. duty cycle...
CCP1CON.4 = Out.0       'Bit 0
CCP1CON.5 = Out.1       'Bit 1
CCPR1L    = Out >> 2    'Bit 2-7
@ INT_RETURN