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'Troubles programming the new 16F877 FLASH parts.'
1999\08\08@055131 by Jim Robertson

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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

Regards,

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

1999\08\08@072911 by Octavio Nogueira

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ProPic 2 is already fixed for this king of problem.

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Octavio Nogueira          / \ AGAINST HTML MAIL
===================================================
.....nogueiraKILLspamspam@spam@propic2.com                  ICQ# 19841898
>From the creator of ProPic, ProPic 2 now much better
New ProPic 2  homepage:      http://www.propic2.com
PIC Programmer for Windows with down to earth price
===================================================
-----Mensagem Original-----
De: Jim Robertson <newfoundspamKILLspamPIPELINE.COM.AU>
Para: <.....PICLISTKILLspamspam.....MITVMA.MIT.EDU>
Enviada em: Domingo, Agosto 08, 1999 07:00
Assunto: Troubles programming the new 16F877 FLASH parts.


> 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
{Quote hidden}

page.
{Quote hidden}

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
{Quote hidden}

1999\08\08@220208 by Jim Robertson

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At 08:25 8/08/99 -0300, you wrote:

So how do I fix mine? I use it for production standard programming.
What is yor recommended solution?

Regards,

Jim


{Quote hidden}

Regards,

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

1999\08\11@012745 by Tony Nixon

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Jim Robertson wrote

> If RB3 is low there is no problem.

Dead right here.

On my new 877 part even with this pin low, the first time it read 0000
all the way through. I erased it and now everything is 3FFF. It even
programs ok now.

> So how do I fix mine? I use it for production standard programming.
> What is yor recommended solution?

The simplest way I could find to modify the programming socket and still
allow programming of other PIC and EEPROMs was to rotate 18 pin PICs 180
degrees. This then swaps VccP and ground and therefore puts ground on
RB3 of the F8xxx parts. Minor PCB changes are needed to swap RB6, RB7
and VPP.

The short cut is to put a 10K resistor from RB3 to ground, cut the VccP
track to this pin, and have a switch or link to connect/disconnect this
pin to VccP.

--
Best regards

Tony

1999\08\11@015907 by Jim Robertson

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At 15:24 11/08/99 +1000, you wrote:
{Quote hidden}

Octavio's solution was to add a RC network and effectively delay the VDD
rise on the LVP pin. This I surmise allows the chip to enter the high voltage
program mode and once safely in this mode the LVP pin doesn't matter any
more.

I added a separate VDD switching transistor and a pull-down resistor on my
second generation PCBs.

Jim

>--
>Best regards
>
>Tony
>
Regards,

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

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