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PICList Thread
'Programming the PIC16F877'
2000\04\03@093452 by naxel

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Greetings to all PIClisters,

I have recently developped a PIC programmer circuit, based on Taits'
design, which worked fine for a PIC16F84. The problem occured when I
tried to program a brand new PIC16F877. At that time, I had no idea of
the LVP ability (I know, I know, RTFM next time :) ), so RB3 was
unconnected. The programming was successful (or so it seemed), but
something weird happened then. All ports of the PIC16F877 that were
configured as outputs, could not rise their voltage to +5. To my
understanding, the PIC is now useless, blown, and that has something to
do with the programming process and the RB3 pin. Later, I found out
about disabling the LVP from the configuration word, but that applies to
all programming attempts after the first.

What should I do with the RB3 pin in order to successfully program the
PIC16F877 for the first time, when all I have is a high voltage
(12-14Volt) programmer (except from obtaining/building a LVP
programmer)?
I desperately need a solution for my final project in university.
Any advice or reference (or good news about the blown chip :) ) is
welcome.

Thank you all in advance.

Nickolas Axelos

2000\04\03@191028 by Tony Nixon

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Nickolas Axelos wrote:

> What should I do with the RB3 pin in order to successfully program the
> PIC16F877 for the first time, when all I have is a high voltage
> (12-14Volt) programmer (except from obtaining/building a LVP
> programmer)?
> I desperately need a solution for my final project in university.
> Any advice or reference (or good news about the blown chip :) ) is
> welcome.
>
> Thank you all in advance.
>
> Nickolas Axelos

Use a 10K resistor from RB3 to +5V and a 100N cap from RB3 to GND.

--
Best regards

Tony

http://www.picnpoke.com
spam_OUTsalesTakeThisOuTspampicnpoke.com

2000\04\03@234954 by Byron A Jeff

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>
> Nickolas Axelos wrote:
>
> > What should I do with the RB3 pin in order to successfully program the
> > PIC16F877 for the first time, when all I have is a high voltage
> > (12-14Volt) programmer (except from obtaining/building a LVP
> > programmer)?
> > I desperately need a solution for my final project in university.
> > Any advice or reference (or good news about the blown chip :) ) is
> > welcome.
> >
> > Thank you all in advance.
> >
> > Nickolas Axelos
>
> Use a 10K resistor from RB3 to +5V and a 100N cap from RB3 to GND.

Interesting. I was just re-reading the 16F87X programming specification and
I just don't see any reference to RB3 when high voltage programming the
part.

I ask because one of my students is at the point where she is trying to
program a 16F87X with a standard Tait style programmer. The programmer
does 16F84's just fine and we've modified the code to substitute a 0x18
begin programming only cycle instead of a 0x08 Begin programming erase
cycle which is simply a begin programming command for the 16F84.

The circuit you show above would pull RB3 from 0 to 5 volts. But is this
necessary if MCLR is going from 0 to 13V?

Look forward to your response.

BAJ

2000\04\04@003101 by Tony Nixon

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Byron A Jeff wrote:
> > Use a 10K resistor from RB3 to +5V and a 100N cap from RB3 to GND.

> The circuit you show above would pull RB3 from 0 to 5 volts. But is this
> necessary if MCLR is going from 0 to 13V?

It holds RB3 low during powerup only. Sometimes the chip won't program
in HV mode when LVP is enabled (default), but it may be a problem only
if this pin is floating. I have tried both ways, and have been caught
out leaving RB3 unconnected, but the RC approach seems to work. You can
see the same circuit in the ROMzap PDF file.

--
Best regards

Tony

http://www.picnpoke.com
.....salesKILLspamspam@spam@picnpoke.com

2000\04\04@015122 by Jim Robertson

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At 11:48 PM 4/3/00 -0400, you wrote:
>>
>> Use a 10K resistor from RB3 to +5V and a 100N cap from RB3 to GND.
>
>Interesting. I was just re-reading the 16F87X programming specification and
>I just don't see any reference to RB3 when high voltage programming the
>part.
>
>
>The circuit you show above would pull RB3 from 0 to 5 volts. But is this
>necessary if MCLR is going from 0 to 13V?
>
>Look forward to your response.
>
>BAJ

This is what I sent to the piclist back in August 1999.

<Quote>

Hi Folks,

Here is the results of some experimenting with the new 16F87x flash parts.
There is a hidden problem with programming these parts and it relates to
the low voltage program mode and the low voltage program control pin RB3.
The type of programming problems I found are similar to those reported on
the piclist by several others.

When these parts a blank (like when new) or any other time the when the LVP
config bit is programmed as a '1' the state of RB3 becomes an issue. It
must NOT
be tied high as VDD rises or unpredictable results occur. I could not get any
satisfaction trying to read or program a part in this condition. Exactly
why I
cannot say. It appears that the chips cannot enter either the low or high
voltage
programming state.  This condition is not documented in the programming
specs so
we are left to wonder.

If RB3 is low there is no problem.

It would not be a good idea to leave RB3 floating as it is an input. I
believe this
may also cause unpredictable results but based on my tests they are not as
common as
when RB3 is held high.

The implications of this are:

1) Some programmers will not be able to program these flash parts unless
modified.
Three programmers in this boat include the propic II, Multi picpro and the
first
release of my own warp-13 (there are details of work arounds on my web page.
The newer Warp-13a has a hardware fix.) No doubt there are other
programmers in
this group.

2) Most programmers should have a resistor fitted to ground on RB3 to
prevent this
input from floating.

3) ICSP will need to be modified to allow for the role of RB3. For many
apps 5-wire ICSP
will need to became 6-wire ICSP with RB3 also connected. If the target circuit
holds RB3 low this will not be required.

4) Care must be taken to ensure that the circuit on a target board ICSP
allows for
RB3 to be pulled low via the programmer.

I believe when these considerations are taken the problems with programming
the flash
parts will disappear as they have for me.

Jim

</quote>

Octavio (PROPIC II) also had discovered this problem independently from
myself and Tony's
solution is actually originally from Octavio who told me in private email
(after I
had posted the above) and I told Tony in a phone conversation. My solution
was to add a
separate transistor switching stage to the RB3 pin.



Regards,

Jim Robertson
NEWFOUND ELECTRONICS
________________________________________
Email: newfoundspamKILLspampipeline.com.au
http://www.new-elect.com
MPLAB compatible PIC programmers.
________________________________________

2000\04\04@062536 by briang

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In-Reply-To: <.....38E96746.59DA0082KILLspamspam.....eng.monash.edu.au>

Tony Nixon <EraseMETony.Nixonspam_OUTspamTakeThisOuTENG.MONASH.EDU.AU> wrote:
> Byron A Jeff wrote:
> > > Use a 10K resistor from RB3 to +5V and a 100N cap from RB3 to GND.
>
> > The circuit you show above would pull RB3 from 0 to 5 volts. But is this
> > necessary if MCLR is going from 0 to 13V?
>
> It holds RB3 low during powerup only. Sometimes the chip won't program

Why can't you just pull RB3 down with a resistor?
Why does it need to go high after it's been low during power up?

Brian Gregory.
briangspamspam_OUTcix.co.uk

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