[sdiy] Getting dsPICs talking

[Stewart Pye]

Hi Neil,

The 33FJ128GP802 comes in a 28 pin DIP package too. I assume this is 
what Tom's using...

Cheers,
Stewart.




Neil Johnson wrote:
> Hi Tom,
>
>> I'm finally into the construction stage of my "Protowave" monosynth 
>> project. The synth uses two dsPIC 33FJ128GP802 processors for its 
>> voice, followed by analog VCF/VCA.
>> One of these uPs is dedicated to production of audio and can generate 
>> two oscillators at 62.5KHz (the "Sources uP"). The second uP is 
>> dedicated to modulation and deals with all the envelopes, LFOs etc. 
>> The final sample rate for this hasn't been determined, but is likely 
>> to be around 10KHz. Both processors are controlled via an SPI link 
>> from a third processor which deals with MIDI, scans the keyboard and 
>> reads the panel controls.
>
> Couple thoughts:
>
> 1/ QFN package ... bit tricky to hand solder, and no use for rework.  
> What about TQFP package?
>
> 2/ You have two SPI peripherals.  You say one is already assigned to 
> the controller comms.  So how about using the second as a dedicated 
> link?  2 data values sampled at 10kHz, even at 16 bits resolution you 
> would only need 320kb/s (40kB/s), and by the looks of it those SPI 
> peripherals can handle 16-bit transfers directly.  So in the Sources 
> uP you have an interrupt handler hanging off the SPI transfer complete 
> interrupt, and update the respective modulation value with the new 
> sample.  For simplicity, use 15-bit values and use the top bit to 
> indicate the destination (e.g., 0 = pitch, 1 = waveshape).  If you 
> have more channels then sacrifice a few more bits for address.
>
> Cheers,
> Neil
> -- 
> http://www.njohnson.co.uk
>
>
>
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