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'ICSP for 16F877'
1999\10\12@140235 by Dave Johnson

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This may be a silly question, but I gotta ask:

I'm building a cable for in-circuit programming of a 16F877. But that
chip has 2 Vdd pins and 2 Vss pins. Does it matter which ones I use? (My
guess is it doesn't matter, that they're connected internally.) If anyone
knows for sure, please let me know.

Dave Johnson

1999\10\12@141704 by Andy Kunz

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>chip has 2 Vdd pins and 2 Vss pins. Does it matter which ones I use? (My

Yes, it matters, and the answer is BOTH!

Andy

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1999\10\12@150941 by Erik Reikes

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At 02:14 PM 10/12/99 -0400, you wrote:
>>chip has 2 Vdd pins and 2 Vss pins. Does it matter which ones I use? (My
>
>Yes, it matters, and the answer is BOTH!
>
>Andy
>

I'm planning on implementing this feature on a 16F876.  I was hoping to use
the LVP mode so as to get by with only three connections.  Has anyone on
the list actually implemented this successfully?  I will try it as soon as
time permits with my parallax programmer, but I'm not sure it supports this
mode.  It seems to me if I jumper the PGC and PGD pins to the proper pins
of my programmer and give it 5 volts it should work.

Thanks in advance.

-Erik Reikes

1999\10\12@154713 by wzab

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On Tue, Oct 12, 1999 at 02:14:49PM -0400, Andy Kunz wrote:
> >chip has 2 Vdd pins and 2 Vss pins. Does it matter which ones I use? (My
>
> Yes, it matters, and the answer is BOTH!

Where can I find more detailed info about these pins? In the data sheet I couldn
't
find any information about them. Does one pair of them is used for analog
part of the chip (ADC) and the another for digital? Or maybe one pair
is reserved for data EEPROM? Do they are shorted inside of the circuit?
I've observed problems with data EEPROM programming in my programmer,
could it be caused by the use of one only pair of Vdd/Vss pins?
--
                       Wojciech Zabolotny
                       http://www.ise.pw.edu.pl/~wzab

http://www.debian.org  Linux - free OS for free people!

1999\10\12@171721 by Dave Johnson

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Andy Kunz wrote:

>Yes, it matters, and the answer is BOTH!
Why? Aren't they connected internally? Inquiring minds want to know :-)

Another wrinkle: I was hoping to use the same cable for a 16C774
(whenever I can get my hands on one), but on that chip the 2 pairs are
different, one pair is analog Vdd and Vss.

I should make one more thing clear: on my board, they're connected
together (although with some filtering on the "analog" pair), so my
question is really about which pins to bring out of the programmer
(PicStart+).

Dave Johnson

1999\10\12@233443 by Jim Robertson

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At 12:13 12/10/99 -0700, you wrote:
>At 02:14 PM 10/12/99 -0400, you wrote:
>>>chip has 2 Vdd pins and 2 Vss pins. Does it matter which ones I use? (My
>>
>>Yes, it matters, and the answer is BOTH!
>>
>>Andy
>>
>
>I'm planning on implementing this feature on a 16F876.  I was hoping to use
>the LVP mode so as to get by with only three connections.  Has anyone on
>the list actually implemented this successfully?  I will try it as soon as
>time permits with my parallax programmer, but I'm not sure it supports this
>mode.  It seems to me if I jumper the PGC and PGD pins to the proper pins
>of my programmer and give it 5 volts it should work.
>
>Thanks in advance.
>
>-Erik Reikes

The parallax programmer unfortunately sources the VDD though a single I/O pin
of the PIC firmware chip. There is no transistor/FET buffering and if you
look at the programming specs you will see that this condition is way out of
spec. Personally, I could not trust the parallax programmer to reliably
program (I.E. over time) the flash parts however you can always power the
target circuit to supply the 5V (as it seems you are planning) and get around
this problem.

More important to note is that if the LVP pin is raised simultaneously with
VDD, the flash parts lock-up and you cannot enter the program mode. There
must
be a delay before raising LVP. This can be done with a simple RC network
as done on the PROPIC II programmer.

If you are powering the DUT from the target board then I would think that
connecting the programmer's switched VDD to the LVP would work and solve both
problems together.








Regards,

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

1999\10\13@100218 by Andy Kunz

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>Another wrinkle: I was hoping to use the same cable for a 16C774
>(whenever I can get my hands on one), but on that chip the 2 pairs are
>different, one pair is analog Vdd and Vss.

I have treat them as AVdd and AVss anyway.

No, I don't believe they are connected internally.

Yes, we changed a Parallax programmer to only put 5V on the line and
modified it to work on RB.3 in LVP mode - it works.  We are planning on
using this to burn already-installed equipment in a TV set (http://www.icommsys.com).

Andy

==================================================================
Eternity is only a heartbeat away - are you ready?  Ask me how!
------------------------------------------------------------------
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EraseMEandyspam_OUTspamTakeThisOuTmontanadesign.com  http://www.montanadesign.com - Electronics
==================================================================

1999\10\13@105050 by wzab

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On Wed, Oct 13, 1999 at 01:39:23PM +1000, Jim Robertson wrote:
> More important to note is that if the LVP pin is raised simultaneously with
> VDD, the flash parts lock-up and you cannot enter the program mode. There
> must
> be a delay before raising LVP. This can be done with a simple RC network
> as done on the PROPIC II programmer.
>
> If you are powering the DUT from the target board then I would think that
> connecting the programmer's switched VDD to the LVP would work and solve both
> problems together.

What does it mean that "flash parts lock-up"? Is it possible that code EEPROM wo
rks
but data EEPROM doesn't? I've observed such a strange behaviour in my programmer
(http://www.ise.pw.edu.pl/~wzab/picprog/picprog.html).
I have modified the PICPRG2.2 software for 16F877, and code was programmed perfe
ctly,
but the data EEPROM was always read as "0" (I reported it to the piclist a few
weeks ago).

--
                       Wojciech Zabolotny
                       http://www.ise.pw.edu.pl/~wzab

http://www.debian.org  Linux - free OS for free people!

1999\10\14@161138 by Erik Reikes

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At 09:53 AM 10/13/99 -0400, you wrote:
>>Another wrinkle: I was hoping to use the same cable for a 16C774
>>(whenever I can get my hands on one), but on that chip the 2 pairs are
>>different, one pair is analog Vdd and Vss.
>
>I have treat them as AVdd and AVss anyway.
>
>No, I don't believe they are connected internally.
>
>Yes, we changed a Parallax programmer to only put 5V on the line and
>modified it to work on RB.3 in LVP mode - it works.  We are planning on
>using this to burn already-installed equipment in a TV set (http://www.icommsys.com).
>
>Andy
>

Interesting... I tried yesterday to use the parallax programmer to program
a 16f876 in LVP mode.  I jumpered the following connections from the
programmer : Vdd, Vss, PGC, PGD, and tied the program 'active' pin and Mclr
to 5V.  My programming software claimed there was no part there.  As a
result of our rather narrow design cycle, I have put fixing this off to the
debug phase and any changes for the 2nd turn of the board.  Are there other
pins I need to connect for the parallax programmer to recognize the part?
I'm considering just using some sort of clamp or bed of nails type thing to
go directly onto all pins of the part for our prototypes.  Eventually the
whole circuit will be potted, so I have attempted to bring the appropriate
pins out.

Is there some 'Gotcha!' that I'm not considering for LVP mode?

Thanks.

-Erik Reikes

1999\10\14@161547 by Erik Reikes

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At 01:39 PM 10/13/99 +1000, you wrote:
>At 12:13 12/10/99 -0700, you wrote:
>>At 02:14 PM 10/12/99 -0400, you wrote:
>>>>chip has 2 Vdd pins and 2 Vss pins. Does it matter which ones I use? (My
>>>

......

{Quote hidden}

Wups... Just saw this message before I posted my last (now obsolete)
question.  I will try delaying the tying of the LVP pin high.  I don't plan
to use the parallax programmer for production, it just happens to be the
only one I currently have.

Thanks for the advice.

-Erik Reikes

1999\10\14@164505 by Dave Johnson

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Dave Johnson wrote:

>>Yes, it matters, and the answer is BOTH!
>Why? Aren't they connected internally? Inquiring minds want to know :-)
An update on this: I went ahead and built the cable using only the Vdd
and Vss pair that are the same on both the 16F877 and the 16C774 (pins 31
and 32 on the DIP package), and it works just fine. Again, these are the
pins I brought out of the programmer (PicStart+): on the board, of
course, these pins are also connected to the other pair.

I'm not using LVP, either, I need RB3 for my own devious purposes :-)

Dave Johnson

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