gnupic: RB3/PGM's purpose
Subject:
Re: RB3/PGM's purpose
From:
Byron A Jeff ####@####.####
Date:
6 Nov 2004 16:07:07 +0000
Message-Id: <20041106160701.GB20829@cleon.cc.gatech.edu>
On Fri, Nov 05, 2004 at 10:34:30PM -0700, Greg Hill wrote:
> On Sat, 6 Nov 2004, Antoine wrote:
>
> > I just realized my pic serial programmer similar to a JDM one. I had
> > some problems during realisation and so had to look different schemas to
> > check if mine is good, but finally it's good and works.
> > On many schema the RB3 pin isn't wired, as on my programmer, at school
> > too we build some projects without (the teacher told us don't wire it
> > because we needed pins and it works without, on 16F876cms+LCD
> > 4bits+sensor+relay+BPs+...).
> > But by reading the topic PICs on Linux, I just saw on this link
> > http://www.finitesite.com/d3jsys that the RB3/PGM pin is wired, so I
> > remember me this question for a new time : what is this pin's purpose
> > during the programmation ??
>
> If I remember correctly, that is the pin used during "low voltage
> programming." Some of the newer PIC parts support this programming mode,
> where you apply +5v (?) on the low-voltage programming pin, rather than
> the usual 12v at the regular programming pin.
>
> If you get a part which is configured for low voltage programming, and
> don't connect that pin to something (both while programming and also
> during normal operation) then strange things can happen. What it comes
> down to in the end is this: if your part is configured to enable
> low-voltage programming, either keep that low voltage programming pin tied
> low except when you're programming or change the configuration (turn
> low-voltage programming off in the config word).
Good explanation. One last point that Wouter van Ooijen pointed out to me.
One action that happens during programming is the clearing of the config
word. This happens in both low voltage and high voltage programming mode.
Then you have to reset the part in both modes in order to get back to the
program memory space. The upshot is that even in high voltage programming mode
there are brief times when the chip is erased and...
FOR THAT TIME IT'S IN LOW VOLTAGE PROGRAMMING MODE!
so any noise on the LVP line can get it mixed up. So I always ground the LVP
pin no matter what mode I'm programming in. Note this is for programmers
only. In normal operation, if the part is configured for high voltage
programming, then this isn't a problem.
BAJ
