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'[PIC] PIC no longer wants to program - is it blown'
2005\07\08@070258 by Michael Curtis

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Hello,

I've (successfully, or so I thought) built the TLVP programmer by Byron Jeff.  
With a bit of fiddling I got it going and was happily writing my first PIC
programs using pikdev until two days ago.  After one particular programming
run, the PIC no longer wants to be programmed and no amount of coaxing will
persuade it, it seems.

I know the chip (a PIC16F628) isn't completely broken, as it still runs the
program I last sent it.  Initially I thought it must have been due to some
stray capacitances, so off I went and dutifully checked all that, but the
voltages and capacitance seems fine.  I suspected transmission problems on my
(short, 20cm) cable so I decoupled both data and clock lines.  Still nothing.  
What baffles me most is that it was working fine and now... nothing.  I've
got good voltage swings - from 0V to 5.4V (supply) and the chip is supplied
by a nice, level, regulated lab supply.

I'm basically at the end of my wit here without any further clues.  The only
things I can think of are: have somehow I inadvertently turned on Code
Protection?  is there a way to tell?  Have I somehow broken the little
monster?  Should I be using more grounding pins on the parallel port (only
using one)?  Have I managed to switch it out of LVP mode (shouldn't be
possible)

Any help here would be appreciated ;).

Michael Curtis
2nd Yr Mechatronics Engineering Student

2005\07\08@073017 by Wouter van Ooijen

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> Have I managed to switch it out of LVP mode
> (shouldn't be possible)

have you enabled internal MCLR?

BAY: can your programmer program a chip configured with internal MCLR?

Wouter van Ooijen

-- -------------------------------------------
Van Ooijen Technische Informatica: http://www.voti.nl
consultancy, development, PICmicro products
docent Hogeschool van Utrecht: http://www.voti.nl/hvu


2005\07\08@074610 by Jan-Erik Soderholm

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Michael Curtis wrote :

> have somehow I inadvertently
> turned on
Code Protection?

An "Erase All" would clear that
anyway.

> is there a
way to tell?

If you can read it or not.
But then you need a *known*
good
programmer, of course.

> Have I managed to switch it out of LVP
mode
> (shouldn't be possible)

Why isn't that possible ? It depends
on what you write to the CONFIG reg.
But then, an "Erase All" will
switch it
back to LVP mode...


Best Regards,
Jan-Erik.



2005\07\08@075055 by Michael Curtis

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On Fri, 08 Jul 2005 23:30, Wouter van Ooijen wrote:
> > Have I managed to switch it out of LVP mode
> > (shouldn't be possible)
>
> have you enabled internal MCLR?
No.  I should now report that I got it to read & program (once), yet
subsequent reads and attempts to get the chip identity now fail.

....
Further testing reveals this: using either pikdev or picprg seem to mess up
the chip so that it can no longer be programmed.  The chip needs a complete
reset (power off, wait 30s, power on) before it will behave itself, only
prog84 will then talk to it.  As these programs previously worked, I'm
guessing that these two are allowing my program to briefly start* before
going into program mode, which causes the hardware to act "strange".  Is this
even possible?  I'll test by reflashing the chip tomorrow but it's late
downunder now.

* the MCLR is only bought high by the programmer, not internally.

Michael Curtis

2005\07\08@075147 by Michael Curtis

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On Fri, 08 Jul 2005 23:46, Jan-Erik Soderholm wrote:

>
> > Have I managed to switch it out of LVP
>
> mode
>
> > (shouldn't be possible)
>
> Why isn't that possible ? It depends
> on what you write to the CONFIG reg.
> But then, an "Erase All" will
> switch it
> back to LVP mode...
The datasheets suggest that the LVP bit cannot be changed when programming in
LVP mode.  As I'm programming in LVP mode, I shouldn't be able to change this
bit, right...?

2005\07\08@080326 by olin piclist

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Michael Curtis wrote:
> Further testing reveals this: using either pikdev or picprg seem to
> mess up the chip so that it can no longer be programmed.  The chip
> needs a complete reset (power off, wait 30s, power on) before it will
> behave itself, only prog84 will then talk to it.  As these programs
> previously worked, I'm guessing that these two are allowing my program
> to briefly start* before going into program mode, which causes the
> hardware to act "strange".  Is this even possible?  I'll test by
> reflashing the chip tomorrow but it's late downunder now.

Are you remembering to hold the PGM pin low during high voltage programming?

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

2005\07\08@080734 by Jan-Erik Soderholm

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pikdev, picprg, prog84...

What a mess... :-)

Why not simply use a
*single* setup that
is documented to work ? How is you
going to know if
it's the PIC, the
programmer or the software ?

> The datasheets
suggest that the LVP bit cannot
> be changed when programming in LVP
mode.

Yep, of course. Sorry...  :-)

Jan-Erik.



2005\07\08@080846 by Michael Curtis

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On Sat, 09 Jul 2005 00:03, Olin Lathrop wrote:

> Are you remembering to hold the PGM pin low during high voltage
> programming?
I'm doing low voltage programming.  I'm beginning to think this may be the
root of all evil....

Michael Curtis

2005\07\08@081952 by Michael Rigby-Jones

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>-----Original Message-----
>From: spam_OUTpiclist-bouncesTakeThisOuTspammit.edu [.....piclist-bouncesKILLspamspam@spam@mit.edu]
>Sent: 08 July 2005 13:07
>To: piclistspamKILLspammit.edu
>Subject: Re: [PIC] PIC no longer wants to program - is it blown?
>
>
>On Sat, 09 Jul 2005 00:03, Olin Lathrop wrote:
>
>> Are you remembering to hold the PGM pin low during high voltage
>> programming?
>I'm doing low voltage programming.  I'm beginning to think
>this may be the
>root of all evil....

IMHO it is.  Unless you have a real need for low voltage programming then avoid it.  It uses up a valuable pin and just causes more headaches than it's worth.  There are so many cheap high voltage programmer designs around that you can either build or buy that using LVP just for the sake of a simpler programmer is not worthwhile.

Mike

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2005\07\08@083640 by Stef Mientki

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>....
>Further testing reveals this: using either pikdev or picprg seem to mess up
>the chip so that it can no longer be programmed.  The chip needs a complete
>reset (power off, wait 30s, power on) before it will behave itself, only
>prog84 will then talk to it.  As these programs previously worked, I'm
>guessing that these two are allowing my program to briefly start* before
>going into program mode, which causes the hardware to act "strange".  Is this
>even possible?
>
Yes, about 3 years ago I posted the same weird phenomena with the 16F84,
I even had to let it rest for about 24 hours !!

Stef Mientki

>  
>

2005\07\08@084406 by Peter van Hoof

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A possible answer found on the net
http://www.htsoft.com/forum/all/showflat.php/Cat/0/Number/15926/Main/15867

If you have the oscillator configured for INTRC and the MCLR pin as an I/O pin.
In this situation your programmer MUST raise Vpp before Vdd, as specified by
Microchip. If your programmer does do this, then make sure you have no
capacitance on the MCLR pin that could slow down the rise of Vpp.

hope this helps

Peter van Hoof


{Original Message removed}

2005\07\08@090035 by Michael Curtis

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On Sat, 09 Jul 2005 00:44, Peter van Hoof wrote:
> A possible answer found on the net
> http://www.htsoft.com/forum/all/showflat.php/Cat/0/Number/15926/Main/15867
>
> If you have the oscillator configured for INTRC and the MCLR pin as an I/O
> pin. In this situation your programmer MUST raise Vpp before Vdd, as
> specified by Microchip. If your programmer does do this, then make sure you
> have no capacitance on the MCLR pin that could slow down the rise of Vpp.
Aha!  I'm using INTOSC but not MCLR as I/O (although I am using TMR1 and CCP
as described in the post, which may be significant), but definitely reversing
the order makes allows me to read from the chip again. Thanks!

Michael Curtis

2005\07\08@090049 by John J. McDonough

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----- Original Message -----
From: "Michael Curtis" <.....listsKILLspamspam.....moltenmercury.org>
Subject: Re: [PIC] PIC no longer wants to program - is it blown?

> prog84 will then talk to it.  As these programs previously worked, I'm
> guessing that these two are allowing my program to briefly start* before
> going into program mode, which causes the hardware to act "strange".  Is
> this
> even possible?  I'll test by reflashing the chip tomorrow but it's late

If your program uses RB6/RB7 as outputs, a programmer (or capacitance on PGM
or !MCLR) which allows the program to run long enough to get the port
initialized will prevent the part from being programmed.

In HVP, this is the reason for the requirement on the risetime on !MCLR.
The pin needs to go from Vss to Vpp without spending any significant amount
of time around Vdd.  With LVP, it has to do with the timing between !MCLR
and PGM, which is a little messier.  If you set the power up timer on you
get a little more elbow room here (the next time you program!).  But
basically, you need to get PGM high before !MCLR has spent more than a few
of clocks around Vdd.  If the chip already has the power up timer enabled,
you get a few clocks plus 72 ms.

--McD

2005\07\08@090113 by John J. McDonough

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----- Original Message -----
From: "Michael Curtis" <EraseMElistsspam_OUTspamTakeThisOuTmoltenmercury.org>
Subject: Re: [PIC] PIC no longer wants to program - is it blown?


> I'm doing low voltage programming.  I'm beginning to think this may be the
> root of all evil....

Exactly

--McD

2005\07\08@094739 by Maarten Hofman

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> > I'm doing low voltage programming.  I'm beginning to think this may be the
> > root of all evil....
>
> Exactly

Not entirely true. This same problem can occur in High Voltage
Programming, as it did to me. There seems to be some combination of
PORTB settings, internal oscillation settings and "use reset as an I/O
pin" settings that cause the 16F628 to not listen to programming
software that is liberal with the specifications. Switching to
stricter programming software usually resolves the issue.

Greetings,
Maarten Hofman.

2005\07\08@201352 by Byron A Jeff

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On Fri, Jul 08, 2005 at 01:30:17PM +0200, Wouter van Ooijen wrote:
> > Have I managed to switch it out of LVP mode
> > (shouldn't be possible)
>
> have you enabled internal MCLR?
>
> BAY: can your programmer program a chip configured with internal MCLR?

Yes. The wiring will control Vdd and allow for the proper sequencing.

The software is another matter however.

BAJ

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