Greetings all,

I'm looking for some guidance in choosing between a PIC18F device
and a dsPIC30F device for a battery-powered application that's in
a very early stage of development-- specifically, any solid
information on relative current consumption at equal levels of
throughput.  The current-hogginess of dsPICs has been discussed
several times on the list in recent weeks, and I don't want to
make a design decision I'll end up regretting: battery life is
important.

This is a digital signal processing application which will be
very math-intensive: each sample (at a 10 KHz sampling rate) will
involve an A/D conversion, a 32x32 unsigned multiply, and several
dozen additions, subtractions, copies and bit shift operations,
all with 64-bit words.  There is very little byte-level
processing or bit-flipping involved in the application, and what
little of it there is, is done at background level (i.e., not at
sampling rate) and is very non-time-critical.  I've done some
exploratory coding and simulation with MPSIM, enough to determine
that a PIC18F252 running at 32 MHz (8 MHz crystal with 4X PLL)
would be adequate for the job.

However, at a quick glance, this would seem an ideal application
for a dsPIC30F3013: with the dsPIC's longer word length, and
consequently higher throughput-per-instruction in math
operations, I would expect to be able to reduce the clock
frequency significantly (maybe by a factor of two?) relative to
what I'd need for the PIC18F-- and perhaps even more, if I can
make good use of the dsPIC's DSP hardware/software resources.

So my concern (prompted by recent PICLIST discussions) is, is
dsPIC current consumption so wretched that a dsPIC30F3013 would
be likely to draw more current than a PIC18F here, even though
clocked at a much lower rate?

My vague, uninformed, totally off-the-wall WAG impression is that
the current consumption of the two approaches will probably be
approximately equal-- and if it is, I'll probably choose the
dsPIC30F simply because I'm eager to begin using these devices
and this project would be as good an opportunity as any.  But if
one approach is likely to give dramatically better battery life
than the other, then that's going to have to be the deciding
factor.

Anybody have any guidance on this?  It's going to be several
weeks before I can conduct a side-by-side "shootout" between the
two processors myself, and until then I'm just guessing.

Thanks in advance,

Dave D.

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