16F628 in-circuit programming problem

Started by leon_heller February 13, 2005
At 04:03 AM 2/15/2005, Vasile Surducan wrote:
> >
> > I offer caution as the negative rail of the PC Com Port, nominally
> > -8 VDC,
> > is used as ground on the programmer and this is fine so long as the
> > programmer is isolated from other circuitry. However, in using the
> > ICSP connector to wire to a PIC in a circuit that is referenced to
> > ground will cause the PC Com port's negative rail to be connected to
> ground.
> > The programmer will not work.
>
> Such remark comming from a teacher makes me at least to smile. The
>programmer in discution is not a debugger nor a developing board
>which is permanently connected to a computer port.
>The user application ground have nothing to do with the computer
>ground. It might be connected to any potential comming from the RS232
>lines from the computer.

Actually, I suspect he speaks from direct experience. If a person is using
ICSP while developing a project, that person probably has test equipment
connected to the circuit. A grounded scope probe is all that it takes to
make the programmer fail to work.

I don't know about you, but I generally have a large number of devices
connected to my prototype circuits. There is usually always a scope hooked
up (may be just the ground lead most of the time - I tend to use a scope
instead of a multi-meter), many of my circuits use a serial port (also
grounded via the PC it is connected to), etc. Trying to use a JDM
programmer in-circuit on those projects will not work.

Finally, keep in mind that his normal audience are college students. They
don't have the benefit of years of experience and might have a very hard
time figuring out why the chip isn't programming. Quite frankly, students
simply don't need that kind of aggravation.

dwayne --
Dwayne Reid <>
Trinity Electronics Systems Ltd Edmonton, AB, CANADA
(780) 489-3199 voice (780) 487-6397 fax

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--- In , Dwayne Reid <dwayner@p...> wrote:
> At 04:03 AM 2/15/2005, Vasile Surducan wrote:
> > >
> > > I offer caution as the negative rail of the PC Com Port,
nominally
> > > -8 VDC,
> > > is used as ground on the programmer and this is fine so long
as the
> > > programmer is isolated from other circuitry. However, in using
the
> > > ICSP connector to wire to a PIC in a circuit that is
referenced to
> > > ground will cause the PC Com port's negative rail to be
connected to
> > ground.
> > > The programmer will not work.
> >
> > Such remark comming from a teacher makes me at least to smile.
The
> >programmer in discution is not a debugger nor a developing board
> >which is permanently connected to a computer port.
> >The user application ground have nothing to do with the computer
> >ground. It might be connected to any potential comming from the
RS232
> >lines from the computer.
>
> Actually, I suspect he speaks from direct experience. If a person
is using
> ICSP while developing a project, that person probably has test
equipment
> connected to the circuit. A grounded scope probe is all that it
takes to
> make the programmer fail to work.
>
> I don't know about you, but I generally have a large number of
devices
> connected to my prototype circuits. There is usually always a
scope hooked
> up (may be just the ground lead most of the time - I tend to use a
scope
> instead of a multi-meter), many of my circuits use a serial port
(also
> grounded via the PC it is connected to), etc. Trying to use a JDM
> programmer in-circuit on those projects will not work.
>
> Finally, keep in mind that his normal audience are college
students. They
> don't have the benefit of years of experience and might have a
very hard
> time figuring out why the chip isn't programming. Quite frankly,
students
> simply don't need that kind of aggravation.

Dwayne, like usually you have (partially) right.
However just try to remind you that you're already on the mined
field when trying to program a PIC soldered on a board with your
scope probe ground connected to the board's ground. Immagine just
that your scope is plugged on other mains phase than your computer.

It's a simple thing which any student (remember: a future engineer)
must know it. Like it must know that this was one reasons why
Tektronics has developed the multi channel scope with isolated
grounds.
A student which is programming with JDM or other programmer chosen
from the thousands, and doesn't know why is programming when is
programming and when not, is not much happy than one who knows those
things. A student which has no time to discover the problem becomes
usually our boss. And then he will never have enough time.

BTW, I have some projects where the PIC is floated on the mains, but
I never tried an ICSP with 316 Vpp on it... After the mains is
powered off and disconnected, programming works well. Just an
example.

So the conclusion is simple. Use the right programmer at the right
place, student or old fox engineer.
:) best regards,
Vasile