Searching \ for '[PIC]:Powering the 16F877 with a 3.5 V, no quartz' in subject line. ()
Make payments with PayPal - it's fast, free and secure! Help us get a faster server
FAQ page: www.piclist.com/techref/power.htm?key=power
Search entire site for: 'Powering the 16F877 with a 3.5 V, no quartz'.

Exact match. Not showing close matches.
PICList Thread
'[PIC]:Powering the 16F877 with a 3.5 V, no quartz '
2002\05\29@085817 by Leo Dep

flavicon
face
Hi PIClist friend,

I have a working 16F877 powered with a 5VDC, with a 20 Mhz quartz.

Powering the same circuit with a 3.5 VDC, the PIC refuse to start.

Looking with a scope on pin 14, the quartz of  20 Mhz, it oscillate with an
amplitude betveen the  0,8 and 1,9 Volt, and on pin 13 a fixed level of  1,2
Volt.

If  I change the quartz with one of 8 Mhz, I obtain a bigger oscillation
signal, mat not suficient to start the PIC.

I have some spare 74HC14 available, it can be useful?

Regards

Leo

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.


2002\05\29@092122 by Brent A. Crosby

flavicon
face
Did you turn BODEN off?

--- Original Message ---
{Quote hidden}

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.


2002\05\29@100715 by Leo Dep

flavicon
face
Hi Brent

many thanks for your interest and suggestion, I have read the documentation
about the BODEN, but sincerely I do not have understand its meaning.
If the actual circuit work with 5 Volt, why I need to change the BODEN when
I work with a low voltage?

Best regards


{Original Message removed}

2002\05\29@103021 by Alan B. Pearce

face picon face
>I have a working 16F877 powered with a 5VDC, with a 20 Mhz quartz.
>
>Powering the same circuit with a 3.5 VDC, the PIC refuse to start.

I have not checked the data sheet, but is it specified to work at 20MHz on
3.5V. If it is have you set HS mode on the config?

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.


2002\05\29@103436 by Brent A. Crosby
flavicon
face
In my understanding, BODEN will hold the chip in reset if Vcc is too low. Its thresholds are set unconditionally to be compatible with 5v, so if you attempt to run at 3.3, BODEN will always hold the chip in reset.

It would have been more useful to have a BODEN_3.3 and BODEN_5.0, or maybe a BODEN with an adjustable threshold, but Microchip did not do it that way.

Can someone else back me up on clearing BODEN for 3.3v designs? I may be out on a limb here.

--- Original Message ---
{Quote hidden}

>{Original Message removed}

2002\05\29@104104 by Leo Dep

flavicon
face
>In my understanding, BODEN will hold the chip in reset if Vcc is too low.
Its thresholds are set unconditionally >to be compatible with 5v, so if you
attempt to run at 3.3, BODEN will always hold the chip in reset.

Thanks Brent, now it is clear ;-)


>It would have been more useful to have a BODEN_3.3 and BODEN_5.0, or maybe
a BODEN with an >adjustable threshold, but Microchip did not do it that way.

:-((

Now I will make a trial with PCON register bit 0 NOT/BOR

>Can someone else back me up on clearing BODEN for 3.3v designs? I may be
out on a limb here.

....
--- Original Message ---
{Quote hidden}

>{Original Message removed}

2002\05\29@110019 by Olin Lathrop

face picon face
> I have a working 16F877 powered with a 5VDC, with a 20 Mhz quartz.
>
> Powering the same circuit with a 3.5 VDC, the PIC refuse to start.

Just like it's supposed to.  RTFM, figure 15-1 page 150 DS3029C.


*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.


2002\05\29@111206 by Olin Lathrop

face picon face
>>
In my understanding, BODEN will hold the chip in reset if Vcc is too low.
Its thresholds are set unconditionally to be compatible with 5v, so if you
attempt to run at 3.3, BODEN will always hold the chip in reset.

It would have been more useful to have a BODEN_3.3 and BODEN_5.0, or maybe a
BODEN with an adjustable threshold, but Microchip did not do it that way.

Can someone else back me up on clearing BODEN for 3.3v designs? I may be out
on a limb here.
<<

You are right.  You can't use the brownout detect feature with "low voltage"
designs because it will detect a brown out even though the power supply is
correct.

However, this guy's problem runs much deeper.  He is using the PIClist as a
substitute for reading the manual.  Not knowing about brown out detect is a
legitimate problem a newbie might stumble over, but attempting to run a 5V
chip at 3.5V without ever checking the electrical specs is just plain stupid
or lazy.  This is true of ANY chip, even a simple inverter.


*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.


2002\05\29@111751 by Drew Vassallo

picon face
> > I have a working 16F877 powered with a 5VDC, with a 20 Mhz quartz.
> >
> > Powering the same circuit with a 3.5 VDC, the PIC refuse to start.
>
>Just like it's supposed to.  RTFM, figure 15-1 page 150 DS3029C.


Maybe you want a 16LF877.  They should operate down near 2.0 VDC.

--Andrew

_________________________________________________________________
Get your FREE download of MSN Explorer at http://explorer.msn.com/intl.asp.

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.


2002\05\29@130732 by Leo Dep

flavicon
face
>> In my understanding, BODEN will hold the chip in reset if Vcc is too low.
>> Its thresholds are set unconditionally to be compatible with 5v, so if
you
>> attempt to run at 3.3, BODEN will always hold the chip in reset.
>>
>> It would have been more useful to have a BODEN_3.3 and BODEN_5.0, or
maybe a
>> BODEN with an adjustable threshold, but Microchip did not do it that way.
>>
>> Can someone else back me up on clearing BODEN for 3.3v designs? I may be
out
>> on a limb here.
>><<
>
> You are right.  You can't use the brownout detect feature with "low
voltage"
> designs because it will detect a brown out even though the power supply is
> correct.
>
> However, this guy's problem runs much deeper.  He is using the PIClist as
a
> substitute for reading the manual.  Not knowing about brown out detect is
a
> legitimate problem a newbie might stumble over, but attempting to run a 5V
> chip at 3.5V without ever checking the electrical specs is just plain
stupid
> or lazy.  This is true of ANY chip, even a simple inverter.

I do not agree with your way to evaluate people that ask help.
I have asked help because I'm in trouble. You have partially reason saying
from your poin of wiev this is a stupid problem, but I have been evaluate
the possibility to use the 16F877 at lover voltage. On the manual on page
151, table 15.0 DS30292B and in the following page I have understand that
the PIC should be used at lower voltage, and in particular I use the PIC at
3,9 Volt.

Now the problem of the oscillator seem solved, because with a couple of
spare gate of a 74HC14 I have put the oscillator  to work in good shape, but
I would like understand why with a 4 Mhz clock the PIC refuse to start, also
making action on PCON.0  register as suggested by Brent.

If at the end of this discussion the answer is "PIC CANNOT BE USEDWITH POWER
SOURCE LESS THAN 5 VOLT", for me is important, because I can decide to power
in other way.

Regards

Leo

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.


2002\05\29@133234 by Mark J. Dulcey

flavicon
face
Leo Dep wrote:
> Hi PIClist friend,
>
> I have a working 16F877 powered with a 5VDC, with a 20 Mhz quartz.
>
> Powering the same circuit with a 3.5 VDC, the PIC refuse to start.

One problem you will have is that the 16F877 isn't rated to work at 3.5
volts! According to the spec sheet, the minimum voltage is 4.0 volts,
and for 20 MHz operation, the minimum voltage is 4.5 volts. (See the
chart on page 150.) Furthermore, the minimum voltage for the HS
oscillator configuration is 4.5 volts (see page 152); presumably you can
only operate the 16F877 above 4 MHz at 4.0 volts if you use an external
oscillator.

For 3.5 volt operation, you'll need to use a 16LF877. But that part will
limit you to 10 MHz operation. (See the chart on page 150.) And you'll
have to use an external oscillator to get there, since the 16LF877
doesn't support the HS oscillator mode.

The newer 16F877A improves matters slightly; it's rated for full 20 MHz
operation at 4.0 volts. But the 4.5 volt floor on HS oscillator
operation remains.

If you really need to combine that speed of operation with 3.5v
operation, you might want to consider using the 18LF452, if you can get
your hands on any. That part should be good for about 30 MHz at 3.5
volts, and the HS oscillator mode is supposed to work all the way down
to the 2 volt floor.

Others have mentioned the problem with the brown-out detector. The 16F
parts have fixed BODEN thresholds. The 18F series has a programmable
detector with four settings (2.0, 2.7, 4.2, and 4.5 volts), though the
lower two only apply to 18LF parts.

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.


2002\05\29@135514 by Bob Ammerman

picon face
Olin,

Maybe this newbie had no idea that there was any relationship between speed
and voltage. That relationship isn't exactly obvious, and to get it out of
the datasheet you have to interpret some funny looking operating region
graphs which are not, at first glance, intuitive.

Bob Ammerman
RAm Systems

{Original Message removed}

2002\05\29@141144 by Bob Ammerman

picon face
According to the graphs in the datasheet a PICF877-20 is rated at up to
20MHz as long as the voltage is greater than 4.5. It is derated to a maximum
of 16MHz between 4.0 and 4.5 volts. It is not rated to work AT ALL at
voltages below 4.0 volts.

Bob Ammerman
RAm Systems


{Original Message removed}

2002\05\29@142223 by Leo Dep

flavicon
face
> According to the graphs in the datasheet a PICF877-20 is rated at up to
> 20MHz as long as the voltage is greater than 4.5. It is derated to a
maximum
> of 16MHz between 4.0 and 4.5 volts. It is not rated to work AT ALL at
> voltages below 4.0 volts.
>
> Bob Ammerman
> RAm Systems

That means I cannot use directly the 3,9 voltage to correctly power the
16F877,
and as i need speed, in this moment I'm thinking to use a step-up to raise
at 5V
the battery voltage.

Do you have suggestions about the best step up chip, that require minimun
count
of external components?

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.


2002\05\29@150219 by Tal (Zapta)

flavicon
face
There are a bunch of chips to do the job. Some have regulator, some don't
(e.g. http://www.national.com/ds/LM/LM2665.pdf).

Go to http://www.digikey.com and search for 'charge pump' or 'capacitor converter'.

If you want to have it really cheap (for mass production), you can even
build it
yoruself with a bunch of inverters (sorry, don't have the schema, maybe
somebody
on the list knows).

Tal

> {Original Message removed}

2002\05\29@170238 by Olin Lathrop

face picon face
> > > I have a working 16F877 powered with a 5VDC, with a 20 Mhz quartz.
> > >
> > > Powering the same circuit with a 3.5 VDC, the PIC refuse to start.
> >
> >Just like it's supposed to.  RTFM, figure 15-1 page 150 DS3029C.
>
>
> Maybe you want a 16LF877.  They should operate down near 2.0 VDC.

But not at 20MHz.  The fastest speed at 3.5V is attained with the L part,
which is 10MHz.  The lowest voltage you can do 20MHz at is 4.5 volts.


*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.


2002\05\29@171718 by Olin Lathrop

face picon face
> On the manual on page
> 151, table 15.0 DS30292B

You should get the latest data sheet.  I don't know what the differences
are, but I have DS30292C.

> and in the following page I have understand that
> the PIC should be used at lower voltage, and in particular I use the PIC
at
> 3,9 Volt.
>
> ...
>
> If at the end of this discussion the answer is "PIC CANNOT BE USEDWITH
POWER
> SOURCE LESS THAN 5 VOLT", for me is important, because I can decide to
power
> in other way.

I'm not sure what you are trying to do, but tables 15-1 thru 15-4 quite
clearly show the relationship between voltage and maximum frequency.  I
wouldn't know how to explain it any better.  What about them don't you
understand?


*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.


2002\05\29@171726 by M. Adam Davis

flavicon
face
It appears to me on the 877a datasheet that the16f877a can run at 4.0
volts up to 20MHz...

-Adam

Olin Lathrop wrote:

{Quote hidden}

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.


2002\05\29@175615 by Mark J. Dulcey

flavicon
face
M. Adam Davis wrote:
> It appears to me on the 877a datasheet that the16f877a can run at 4.0
> volts up to 20MHz...

True, the 877A (note the A) can do that. The original 877 can't; you
have to supply at least 4.5 volts for 20 MHz operation. (And you still
need 4.5 volts to use the HS oscillator, even on the updated version.)
But the 16F877A is still scarce; most of the parts that people already
have are the original version, not the updated one, and distributors
don't have any 16F877A parts right now.

Another advantage of the 877A, by the way, is that it also has the
comparator / voltage reference module. Supposedly, unlike other parts
with the comparator module, it's disabled at power-on, so you don't have
to change your code. The flash memory is now rated to survive ten times
as many programming cycles. It is also, in theory, slightly cheaper, but
that doesn't mean much when you can't get the parts.

Disadvantages: the device programming specifications have been changed,
so your programmer's software may need updating. The procedure for
writing to flash memory in program code has also changed, so software
that does that will require modification.

Presumably, the older parts will be discontinued once Microchip ramps up
production of the new ones, or at least they'll be priced out of
consideration. After all, you can still buy the original version of the
16F84 ($4.51 for 4 MHz parts at Pioneer), even though the 84A ($3.46)
has been out long enough to itself be obsolete. A 4 MHz 16F627 costs
$1.82, and a 16F628 is $2.07; you'd have to be desperate for 100%
compatibility (replacement for a chip in a system that runs at 6 volts,
perhaps; the newer parts are only specified to 5.5 volts) to actually
buy a 16F84.

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.


2002\05\30@032644 by uter van ooijen & floortje hanneman

picon face
> It appears to me on the 877a datasheet that the16f877a can run at 4.0
> volts up to 20MHz...

So the only ting that is missing is a place where yo can buy an f877a?

Wouter

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email @spam@listservKILLspamspammitvma.mit.edu with SET PICList DIGEST in the body


More... (looser matching)
- Last day of these posts
- In 2002 , 2003 only
- Today
- New search...