Hi all,
I have a dsPIC30F based design where power consumption is critical. But the
very high clock that I need is justified only by a part of the design, i.e.
that I need a 32bit timer with the best time-resolution possible. Basicly
I'm recording when some events take place (timestamp), a bit like a logic
analyzer but the events are considerably less frequent (around 1000Hz max),
however as I said I need very good resolution (around 35-40ns is my goal).

This could be achieved by the dsPIC, pairing Timer2 and Timer3 into a 32bit
timer (or using interrupts to simulate the higher word timer), but the powe=
r
consumption at 25-30MHz is very high, way too high, and SLEEP mode disables
clocks anyway, so forget about using it, and IDLE mode still consumes a lot=
..

I thought about using an external oscillator both as a system clock and as
Timer1 asynchronous input.

Has anyone ever tried to use the Timer1 as a high resolution time stamp
counter, with the DSC most of the time sleeping? Any quirks? Or hints?

This said, I've looked at the data sheets of all the 5V oscillators I could
find, but they consume tens of mA's. Probably they mean only at max output
load, but this is not specified in the data sheet. How much current does a
typical 5V osc really draw? Can you suggest me a 5V osc (best 7.3728MHz) th=
at
draws as little current as possible?

This way I could get timer1 counting cycles (till PR1=3D0x8000 interrupt,
which will wake up the DSC and allow me also to increment with the CPU the
higher bits of the time stamp counter), SLEEP as much as I need, and be
waken up by the timer every 0x8000 cycles or by a CNx event.

Do you think it is achievable?

No I can't use an FPGA, I'd like it, it would be trivial, but it's overkill=
,
I must use what I have (the dsPIC), the most I can do is to opt for an
external oscillator in place of the typical XTAL. No more chips.. although
I wish a high resolution serial time stamp counter IC existed, it would be
very useful for some projects. It would detect edges from its inputs and
record in a FIFO when they took place, then you would load serially this
info back into the DSC/MPU. I doubt such a chip exists (at least at high
resolutions, i.e. tens of ns range), but anyway even if I can't use it for
this project, if such a chip exists I'd like you to tell me! :-)

What about my Timer1 + ext oscillator design.. do you think it's a winner?
I wish I can stay below 10 mA total power consumption.. as I said the 30F
will sleep most of the time, but events must be timed very accurately.

Thanks a lot,
Mario

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