I'd like to share my experience with you about
programming the pic uC.
I made my own test board to experiment the various
functions of the 16F877.I designed it in such a way
that to can program it without removing the pic from
the test bourd(I think it is called In-Circuit Serial
Programming).I use a switch to connect RB6,RB7 and
MCLR to the test board or programmer.I use also
another switch to turn off the power from the other IC
so all PIC pins are free.But the circuit didn't work
in this way.I was wondering why and finally I found
out that when the quartz(4MHz) is disconnected when
the programming is running everything is OK.
So, is there any unusual or it is always necessary to
provide for a switch to disconnect the quartz when
programming.I use PonyProg2000.
dimov stefan wrote:
> So, is there any unusual or it is always necessary to
> provide for a switch to disconnect the quartz when
> programming.
Something doesn't sound right. The crystal oscillator should have no effect
on programming unless the programmer has a VERY long Vpp rise time. What
does your MCLR circuit look like? Is there a cap on MCLR? What are you
doing to keep MCLR at Vdd for normal operation but still allow it to be
raised to Vpp by the programmer?
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> > So, is there any unusual or it is always necessary to
> > provide for a switch to disconnect the quartz when
> > programming.
>
> Something doesn't sound right. The crystal oscillator should
> have no effect on programming unless the programmer has a VERY
> long Vpp rise time.
In my experience this is a normal effect for primitive programming
hardware that is not designed for in-circuit programming.
> > > So, is there any unusual or it is always
> necessary to
> > > provide for a switch to disconnect the quartz
> when
> > > programming.
> >
> > Something doesn't sound right. The crystal
> oscillator should
> > have no effect on programming unless the
> programmer has a VERY
> > long Vpp rise time.
>
> In my experience this is a normal effect for
> primitive programming
> hardware that is not designed for in-circuit
> programming.
>
> Wouter van Ooijen
Maybe the culprit is the programmer I have.It is a kit
bourd which is an universal programmer for PIC,AVR and
EEPROMs with corresponding attachments and probably it
is not designed for ICSP.
The most likely reason for the flaw is,as Olin said,
too long rise time of Vpp.This is discribed in TB016 -
"How to implement ICSP using pic16f8X flash MCUs".
To solve this problem I'm going to use a switch to
connect crystal osc. to ground when programming.
But I'm not completely convinced that this is the
right solution because with the previous circuits I
have made there weren't such problems.I suspect that
the other parts influence to the pic although there
are not powered.But I leave that to you to consider.I
attach the circuit.
