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'[PIC]: P 'Two speed' clock support'
2000\06\28@071846 by D Lloyd

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Hi,

I've been looking towards using a PIC for a 'dual speed' operation; running the
PIC from a (small) battery during a power failure (sleep then wake up, even at
the lower oscillator rate......or maybe run all the time) then resuming full
power operation when power is restored. As things go, the oscillator speed  for
achieving the reduced power mode requirements does not provide enough processing
"oomph" when full power is available. Hence, dual-clock operation would be
beneficial.

I've had a poke around on the mchip site/checked out a few data sheets and I
cannot really find too much information or a specific micro that performs this.
Mitsubishi etc make micros that specifically support this - is it blatantly
obvious how to do this with the PIC and I have missed it, or is it just not
possible?

I've seen a posting where an RC oscillator is used where additional resistance
is switched in and out via an I/O pin (dual speed) but I don't think RC is going
to give me the clock accuracy that is required.

Any comments would be appreciated.

Regards,

Dan

2000\06\28@080106 by Bob Ammerman

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I know that it is possible to run a PIC set to RC mode with an external
oscillator. I am sure some of our hardware experts can tell you how.
Perhaps you can then use real RC for the low speed (assuming you don't need
the timing precision in low-power mode) and an external osc module for high
speed.

One thing to watch out for: when in RC mode there are differences in the
oscillator start up timer, and the timing when coming out of sleep. I'd
recommend the hardware defaulting to RC, then switching to the XTAL under
software control. You are going to have to be very careful about the timing
at the transition point to avoid getting a clock cycle that doesn't meet the
chip's timing.

Bob Ammerman
RAm Systems
(high performance, high function, low-level software)

{Original Message removed}

2000\06\28@081344 by M. Adam Davis

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I believe I've seen oscillators with built in selectable dividers, but I cannot
remember where.  You can use a seperate oscillator and divider, and use a pic
output or two to set the divider when necessary.

-Adam

D Lloyd wrote:
{Quote hidden}

2000\06\28@103525 by D Lloyd

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part 1 2451 bytes content-type:text/plain; charset=us-ascii

Hi,

So it would seem that there is no 'on chip' support for such functionality....
The application is cost sensitive so precludes the use of anything too
messy/complicated/costly externally. That's not to mention the hazards, as Bob
suggested, of dodgy edges.
Looks like another route is necessary.

Thanks again,

Dan




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 |"M. Adam Davis" <spam_OUTadavisTakeThisOuTspamUBASICS.COM>                                    |
 |28/06/2000 13:13                                                        |
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Please respond to pic microcontroller discussion list <.....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU>

To:   PICLISTspamKILLspamMITVMA.MIT.EDU
cc:    (bcc: Dan Lloyd/GBPTD/ABB)
Subject:  Re: [PIC]: P 'Two speed' clock support

Security Level:?         Internal



I believe I've seen oscillators with built in selectable dividers, but I cannot
remember where.  You can use a seperate oscillator and divider, and use a pic
output or two to set the divider when necessary.

-Adam

D Lloyd wrote:
>
> Hi,
>
> I've been looking towards using a PIC for a 'dual speed' operation; running
the
> PIC from a (small) battery during a power failure (sleep then wake up, even at
> the lower oscillator rate......or maybe run all the time) then resuming full
> power operation when power is restored. As things go, the oscillator speed
for
> achieving the reduced power mode requirements does not provide enough
processing
> "oomph" when full power is available. Hence, dual-clock operation would be
> beneficial.
>
> I've had a poke around on the mchip site/checked out a few data sheets and I
> cannot really find too much information or a specific micro that performs
this.
> Mitsubishi etc make micros that specifically support this - is it blatantly
> obvious how to do this with the PIC and I have missed it, or is it just not
> possible?
>
> I've seen a posting where an RC oscillator is used where additional resistance
> is switched in and out via an I/O pin (dual speed) but I don't think RC is
going
{Quote hidden}


part 2 165 bytes content-type:application/octet-stream; (decode)

part 3 2 bytes
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2000\06\28@121220 by Dan Michaels
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Dan Lloyd wrote:
>I've been looking towards using a PIC for a 'dual speed' operation; running the
>PIC from a (small) battery during a power failure (sleep then wake up, even at
>the lower oscillator rate......or maybe run all the time) then resuming full
>power operation when power is restored. As things go, the oscillator speed  for
>achieving the reduced power mode requirements does not provide enough
processing
>"oomph" when full power is available. Hence, dual-clock operation would be
>beneficial.
...........
>

1. Checkout the ICS5xx PLL Clock Multiplier chips from http://www.icst.com/

2. I believe the new Mchp 18Cxxx chips have a configurable PLL clock on
  board.

3. Also, the 16C73/74/.. chips have a 2nd oscillator on board wired to
  pins C0/C1, and which can be used with a 32khz xtal. Can be used with
  sleep mode and any speed xtal on main oscillator.

best regards,
- Dan Michaels
Oricom Technologies
http://www.sni.net/~oricom
==========================

2000\06\28@142601 by dal wheeler

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How much current would an external clock driver w/ selectable dividers draw
as opposed to a "traditional" high-speed crystal w/ pic/sx in sleep mode
when not in use?  Is there such a thing as a selectable divider regular
crystal?  Also I've seen it proposed to switch between low speed RC and high
speed crystal; how can one do that?  Is'nt that a setting burned at program
time?
I
----- Original Message -----
From: "M. Adam Davis" <.....adavisKILLspamspam.....UBASICS.COM>
> I believe I've seen oscillators with built in selectable dividers, but I
cannot
> remember where.  You can use a seperate oscillator and divider, and use a
pic

2000\06\28@213247 by Bob Ammerman

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btw: The PIC18Cxx2 chips support this directly, using an alternate clock on
other pins. But of course 18Cxx2 are not exactly appropriate for
cost-sensitive designs!

Bob Ammerman
RAm Systems
(high performance, high function, low-level software0


{Original Message removed}

2000\06\28@213301 by Bob Ammerman

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----- Original Message -----
From: dal wheeler <EraseMEdwheelerspam_OUTspamTakeThisOuTINSIGHTEK.COM>
To: <PICLISTspamspam_OUTMITVMA.MIT.EDU>
Sent: Wednesday, June 28, 2000 2:18 PM
Subject: Re: [PIC]: P 'Two speed' clock support


> How much current would an external clock driver w/ selectable dividers
draw
> as opposed to a "traditional" high-speed crystal w/ pic/sx in sleep mode
> when not in use?  Is there such a thing as a selectable divider regular
> crystal?  Also I've seen it proposed to switch between low speed RC and
high
> speed crystal; how can one do that?  Is'nt that a setting burned at
program
> time?
> I

This can be done by setting the chip to RC mode, but then driving it with an
external oscillator (_not_ a crystal!). Again, the trick would be to arrange
for 'glitchless' transitions.

Bob Ammerman

> ----- Original Message -----
> From: "M. Adam Davis" <@spam@adavisKILLspamspamUBASICS.COM>
> > I believe I've seen oscillators with built in selectable dividers, but I
> cannot
> > remember where.  You can use a seperate oscillator and divider, and use
a
> pic

2000\06\28@221837 by David Covick

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Dan,

Try this URL.  "Microcontroller controls its own clock speed" One chip and 2
xtals.

http://www.elecdesign.com/magazine/1998/sept0198/ifd/3IFD.pdf

David


{Original Message removed}


'[PIC]: P 'Two speed' clock support'
2000\07\01@065426 by Oliver Broad
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Hi.

I've lost the start of this discussion, which PIC did you intend using,
I've an idea that would work on 16C73 or up possibly.

Use the RC osc, but have a way to trim the frequency in software. A DAC is
probably too expensive but filtering a PWM output might do. Fit a 32KHz
xtal on the timer1 osc. Use the crystal to 'calibrate' the main osc. A
switched resistor would provide the main frequency switch function, keep
the trim down to 10%

Never tried it myself, however I've had the luxury of working on mains
powered projects so far.

Oliver.

2000\07\03@024102 by Gennette, Bruce

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I haven't followed this fully myself, but how about an R-C oscillator with
the R being a light dependant resistor.  Hook an LED up to an output pin and
you can switch the value of the resistor quite a long way. (need to seal the
pair in a light proof manner)

Better informed experts than me can calculate the R-C and wether the LED has
to be attenuated with a filter.

Should give glitch free speed changing as the LED powers up or down.

Bye.

       {Original Message removed}

2000\07\03@033912 by Kevin Blain

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Something I havn't tried <grin> but have dreamt up, is using the new flash
parts...

Seeing as they have self reprogramming, it would be possible to reprogram
the config bits at 2100h onwards to change the part from RC to XT. Ok. Now
the fun bit.

Power a crystal oscillator module from a PIC i/o pin.

Drive a crystal oscillator into a resistor do ground, through a schmitt
trigger inverter into the top of an RC series combination to ground. Then
take the junction from the R and C to the OSC1 pin - with me?

The RC is calculated for your initial frequency in RC oscillator mode. The
pic would wake from sleep, and because the crystal oscillator is switched
off at this point, the R to ground on the input to the schmitt inverter will
cause the output to be a logic 1. This provides the necessary +V to run the
RC oscillator, into OSC1. When powered up, the PIC switches the Oscillator
module on, and then reprograms itself to XT mode. Geddit?

This would be intended for timing sensitive applications, where RC is not
accurate enough, but when low power standy, possibly interrupt or watchdog
wake from sleep is used. Any thoughts?

Kevin.

----- Original Message -----
From: Gennette, Bruce <KILLspambruce.gennetteKILLspamspamTAFE.NSW.EDU.AU>
To: <RemoveMEPICLISTTakeThisOuTspamMITVMA.MIT.EDU>
Sent: Monday, July 03, 2000 7:39 AM
Subject: Re: [PIC]: P 'Two speed' clock support


> I haven't followed this fully myself, but how about an R-C oscillator with
> the R being a light dependant resistor.  Hook an LED up to an output pin
and
> you can switch the value of the resistor quite a long way. (need to seal
the
> pair in a light proof manner)
>
> Better informed experts than me can calculate the R-C and wether the LED
has
> to be attenuated with a filter.
>
> Should give glitch free speed changing as the LED powers up or down.
>
> Bye.
>
>         {Original Message removed}

2000\07\03@034949 by D Lloyd

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Hi,

Thanks to everyone offering suggestions to overcome this problem. Unfortunately
for many of the suggestions, the application is connected to an electricity
meter of which there is no option for a "reset" or "just cycle the power and it
will be fine" and so the solution needed to be absolutely bullet-proof. I can
think of only the (expensive) switched external oscillator or a multispeed micro
being the only real solutions. I'll certainly consider them for other projects,
though!

Thanks again.

Regards,
Dan

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2000\07\03@191929 by Tony Nixon

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picon face
Kevin Blain wrote:
>
> Something I havn't tried <grin> but have dreamt up, is using the new flash
> parts...
>
> Seeing as they have self reprogramming, it would be possible to reprogram
> the config bits at 2100h onwards to change the part from RC to XT. Ok. Now
> the fun bit.
>

You cannot reprogram the CONFIG register from within the PIC.

Actually, on writing this I thought hang on, perhaps you can.

I fired up the ROMzap PCB and wrote a quick Delphi prog to talk to it
and tried to program the config register but no go.

This would make sense because you would then be able to easily defeat a
code protected device.

--
Best regards

Tony

http://www.picnpoke.com
spamBeGonesalesspamBeGonespampicnpoke.com

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2000\07\04@083900 by Andy Howard

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Re. varying clock rate of PICs.

I had a flyer from my local distributor drop through to letterbox today, in
it there is mention of the 16C717, 770 and 771 which include:

"Dual speed oscillator, dynamically toggle operating frequency" and "ER mode
allows adjustment of execution speed using a single resistor"

Cheers

Andy









.

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2000\07\04@143529 by Peter L. Peres

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>electricity meter, bulletproof

Write the clock switching routine such that it also sets OPTION for a
short watchdog timeout before switching, and allow the PIC to be reset by
the watchdog after changing the clock (both ways). You could use a 74S66F
single CMOS chip as clock switch. Just place 120R in series with the other
crystal (the 74S66F has ~60R open). Then the Q rule will cause the crystal
with the higher Q to run the oscillator. That's it. Or almost.

Peter

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2000\07\05@011556 by Harold Hallikainen

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       Though not what was originally requested (2 speed clock with one being
crystal, the other being RC), you could possibly do a 2 speed RC by
connecting another resistor between the RC input of the PIC and an I/O
pin. Make the pin an input for low speed. Program it as a high output
(putting the second resistor in parallel with the first) for high speed.

Harold



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2000\07\05@033325 by D Lloyd

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<snip>

       Though not what was originally requested (2 speed clock with one being
     crystal, the other being RC), you could possibly do a 2 speed RC by
     connecting another resistor between the RC input of the PIC and an I/O
     pin. Make the pin an input for low speed. Program it as a high output
     (putting the second resistor in parallel with the first) for high speed.

<snip>



The main problem with using RC arrangements is that I need a clock drift of sub
     0.5 seconds per day. I was of the opinion that this was not possible with
     RC sources (sorry if this formatting is haywire, Lotus Bloats is having a
     bad day) - certainly not over a wide temperature range?



Thanks, though

Dan

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2000\07\06@140909 by Peter L. Peres

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D Lloyd <dan.lloydEraseMEspam.....GB.ABB.COM> wrote:
>The main problem with using RC arrangements is that I need a clock drift
>of sub 0.5 seconds per day. I was of the opinion that this was not
>possible with RC sources

Wow. 0.5 sec/day is better than 5.8 ppm and that is hard even for a
crystal ? You can achieve 0.5 sec/day with a cheap 32 kHz resonator,
trimmed manually or electronically at factory, aged (baked), and at
relatively constant temperature. A RC oscillator for 5 ppm would probably
be made entirely of noble materials to avoid aging, kept at a regulated
+/- 0.1 degrees temperature at constant pressure, have temperature
compensation (in despite of thermostat) etc.

0.5 sec/day is 0.5/86400 = .0000057870 (5.79 ppm)

Peter

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2000\07\06@140915 by Peter L. Peres

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Harold Hallikainen wrote:
>        Though not what was originally requested (2 speed clock with one
>being crystal, the other being RC), you could possibly do a 2 speed RC by

Which reminds me that I did not see the orignal posting. I suggested using
a 74S66F switch to change crystals, but for RC, is is possible that a
collector-switched bipolar transistor stage will do the trick. This is
pure imagination so far, but it may work. The scheme is:

PIC + parallel resonant crystal + 2 small capacitors connected as usual.

Coupling cap from Xout to base of additional NPN. Emitter of NPN through
~2k7 to GND. Collector of NPN through 10K to PIC IO pin. Collector of NPN
through coupling cap to Xin. Base of NPN polarized from collector through
~150k. The Xin coupling capacitor should be very small (the same order of
magnitude as the crystal 'pi' capacitor on that side).

Now, when the PIC is reset the IO pin is tristate and the NPN collector
has no current into it. The NPN arrangement should allow the PIC Xtal
oscillator to start as usual in Xtal mode. To switch to RC mode, set the
PIC pin to output and HIGH at the same time. Now the NPN stage is biased
and the crystal appears as NFB across its input and output. This will
hopefully stop the crystal oscillation and then the ac coupled 'gate ring'
oscillator formed by the NPN stage its coupling capacitors and the
internal PIC oscillator gate should take over at a frequency that is to be
determined (but should be obscenely low - tens of kHz probably).

Problem: the conducting NPN will draw more current than the PIC ;-)
Solution (?) replace NPN stage with a single tristate inverting CMOS gate
(4S24?F I think - I've never seen one though they certainly exist) and AC
couple its output only this time. Steer the enable pin with the PIC IO
pin.

Last alternative: Use a 'A' series CMOS inverter gate as external inverter
and steer by switching power using PIC IO pin, hoping for sufficient
isolation between in and out for the Xtal to oscillate with power off.

If anyone will have success with this scheme (which I have no time to try
myself) then please report.

Peter

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2000\07\07@033510 by D Lloyd

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part 1 1832 bytes content-type:text/plain; charset=us-ascii

Hi,

I might have been a bit zealous with the 0.5 sec/day. 1 second per day is more
like it, I think. Still not attainable by RC, I think, not over the temp
range.......
I think I'll have to just keep it simple and go for the on board option.

Dan



|------------->
|(Embedded    |
|image moved  |
|to file:     |
|pic20241.pcx)|
|             |
|------------->
 >------------------------------------------------------------------------|
 |"Peter L. Peres" <EraseMEplpspamACTCOM.CO.IL>                                     |
 |06/07/2000 18:24                                                        |
 >------------------------------------------------------------------------|



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Subject:  Re: [PIC]: P 'Two speed' clock support

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D Lloyd <RemoveMEdan.lloydTakeThisOuTspamspamGB.ABB.COM> wrote:
>The main problem with using RC arrangements is that I need a clock drift
>of sub 0.5 seconds per day. I was of the opinion that this was not
>possible with RC sources

Wow. 0.5 sec/day is better than 5.8 ppm and that is hard even for a
crystal ? You can achieve 0.5 sec/day with a cheap 32 kHz resonator,
trimmed manually or electronically at factory, aged (baked), and at
relatively constant temperature. A RC oscillator for 5 ppm would probably
be made entirely of noble materials to avoid aging, kept at a regulated
+/- 0.1 degrees temperature at constant pressure, have temperature
compensation (in despite of thermostat) etc.

0.5 sec/day is 0.5/86400 = .0000057870 (5.79 ppm)

Peter

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2000\07\08@112435 by Peter L. Peres

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>1 sec/day

which is about 12ppm. By looking in Mouser we see a 32kHz crystal that
claims +/- 20 ppm. If you use this one and trim it in factory then you may
have a fair chance. Perhaps you can avoid clock switching completely, and
run your project all the time at 32kHz.  Costs ~= 0.73 in 100's (warning:
I do not have the latest Mouser).

A TCXO (FOX) that requires no trimming and does 2.5 ppm over temperature
and 0.3 ppm over supply will certainly fix your problem, assuming indoor
use (restricted temp. range) at a mere $38.85 ea. in 100's ;-)

Peter

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