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

[cncmachineguy]

Hank you could get the QFP package, 28 pins in a 4mmX4mm space

[HankMcSpank]

Hank you could get the QFP package, 28 pins in a 4mmX4mm space

QFP at 0.5mm pitch is a bit too challenging for my soldering iron..



Just noticed a discrepancy, on the Microchip site ....the 'highlights' of the PIC16Ff1782/3 has 4 x 8 bit timers & 1 x 16 bit timer shown...

http://www.microchip.com/wwwproducts...cName=en552738

but in the datasheet it's only talking of 2 x 8 bit timers & 1 x 16 bit timer...

http://ww1.microchip.com/downloads/e...Doc/41579B.pdf

Bert...re your former post/points, it's late here in the UK, I've now had a couple of beers too....this is challenging for McSpank's grey matter even when sober, so I'll defer until later!

[cncmachineguy]

OMG!!! Hank I would be way challanged using those on 1/4" spade terminals with 14GA wire. LMAO!!!!!

[HankMcSpank]

ok, not running interrupts here, just the bare minimum main loop (as per Bert's proposal)...

tuning_word         VAR word
accumulator         VAR WORD
'
ACCUMULATOR = 0          ' clear down the accumulator before starting.
TUNING_WORD = 1     ' 
'
Main:
ACCUMULATOR = ACCUMULATOR + tuning_word
'
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],PORTC
'
goto main
'
END

not sure if my maths is correct here, but

total number of sine 'slices' = 256 (1 period...ie all the values in the array)

accumulator is 16 bits long therefore counts to 65536 & rolls over

With the tuning word set to 1 (this is the number added to the accumulator on each loop)

My scope measures a waveform frequency of 5.09Hz, therefore...

sampling rate = Frequency/tuning word * accumulator or 5.09/1 * 65536 = 333,578hz ..........or a sampling rate of 333.578khz (ie how often the main loop is erhm looping)

...this actually kinda sucks for a DDS sampling rate (most of the DDS solutions talk of a mega high sampling rate) ....I'm running my PIC at 32Mhz Osc (8mhz * 4 PLL), therefore instruction clock of 8Mhz.



The highest frequency with all the bits in the array being read properly (vs being skipped) is now about 1.3Khz....



Any top tips for getting the effective sampling rate even higher? (ie getting the main loop to run faster)

[mister_e]

Not sure but I feel using something else than LOOKUP may speed up the process... Which PIC you use right now?!?

[HankMcSpank]

I'm using a 16f1828 .

[mister_e]

Is it me or the problem lie in the .HighByte thing?
Lookup Accumulator.HighBYTE, [

It take 256 times BEFORE it goes to the next index. though I may need to sleep.