[sdiy] PIC Wavetable OSC Timing

[William Berzinskas]

nice1..   got the interrupt going with fairly little work..   on to decoding
notes.. thanks a bunch!

----- Original Message ----- 
From: "Fredrik Carlqvist" <ifrc at iar.se>
To: "'William Berzinskas'" <WBERZINSKAS at nc.rr.com>;
<synth-diy at dropmix.xs4all.nl>
Sent: Monday, January 03, 2005 7:03 AM
Subject: RE: [sdiy] PIC Wavetable OSC Timing


>
> If you are using a PIC with a CCP unit, you can use that easier/better
than
> just a timer. The CCP method keeps the overhead to a minimum.
>
> I would use the interrupt from CCP1 in compare mode with the side effect
> enabled: to clear the timer. The only thing you will have to do is to
write
> the interrupt period time into the CCP registers (CCPR1L and CCPR1H).
Every
> time timer 1 reaches the value in the period registers, it will be
> automatically reset and a CCP1IF interrupt will be generated. Inside the
> interrupt service routine, you just read out the next wave value and
output
> it to the R-2R ladder and return.
>
> In the main loop, you keep the period registers CCPR1L and CCPR1H updated.
> Make sure that you never accidentally write zero into them (for example
when
> changing from 0xFF to 0x100 and writing the low byte first)! Polling the
> UART for MIDI data, you will probably need a table to look up appropriate
> interrupt intervals for different MIDI note numbers.
>
> This works the same way on both PIC18 and PIC16 architectures. Using
PIC16,
> I would enable the CCP1IF interrupt only, and poll all other things, like
> MIDI data in for example. Probably, you will have no choise but to write
the
> application in assembly, because the interrupt overhead of a C compiler
> would probably limit the top frequency severely.
>
> On PIC18, I would keep the CCP interrupt at high priority and any other
> interrupts on low.
>
> The following example sets up the CCP and TIMER1 units to form a DCO on a
> PIC16:
>
>   // set up CCP oscillator (PIC16F818)
>   T1CON = 0x01;   // enabled, no prescaler
>   CCP1CON = 0x0B; // special event trigger
>   CCP1IE = 1;
>
> If you need more details, don't hesitate to ask!
>
> Good luck!
>
>
> Fredrik C
>
>
>
> ________________________________
>
> From: owner-synth-diy at dropmix.xs4all.nl
> [mailto:owner-synth-diy at dropmix.xs4all.nl] On Behalf Of William Berzinskas
> Sent: den 29 december 2004 22:52
> To: synth-diy at dropmix.xs4all.nl
> Subject: [sdiy] PIC Wavetable OSC Timing
>
>
> Hey everyone..
>
> I've made a simple wavetable oscillator..  it's got an r-2r ladder and 64
> position waves..  works pretty good for the basic stuff i've got..  got a
> few waveforms in there.. nothing special, just the standard tri/saw/square
> for testing..
>
> can someone explain to me how to setup the timing to be controllable via
> midi..
>
> if i understand correctly, the midi note number would somehow set the
reset
> point on a timer..  the timer would interrupt at a specified freq, and
> output the bits..
>
> assuming i've got that lil theory-ish part right, how to implement it?
>