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'[PIC]: Sources of ISCP problems (was 16f84 Questio'
2002\02\05@150018 by Kevin Olalde

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OK, thanks.  I've had a devil of a time getting consistent ISCP results, so
along with excellent Wouter's suggestions below, are there more 'gotchas'?

Did I read in a thread recently that a fast starting oscillator is also a
potential problem?  Should I ground the OCS1 while programming?

I'm guessing I don't need to tie LVP low if I'm using HVP, correct?

How about breadboards?  Since I'm just starting out, most of my work is done on
these.  Since I've read here that they are 'big capacitors', is this also a
source of problems?  Even if no other part of the circuit is connected to RB6
and RB7.

Finally what about the programmer?  Once ISCP programmer I've tried works about
10% of the time, on 16F84A and 16F628 parts always in HVP mode.  I recently got
a ICD, on the same breadboard, same MCLR > 10K R > VCC, it works 100% percent of
the time on 16F87x parts.  Maybe the inconsistent programmer is getting bit by
the oscillator issue (I'll go try that now)?

Thanks for any thoughts,
Kevin

wouter van ooijen & floortje hanneman wrote:
> sources of ICSP trouble:
> - load on /MCLR (esp. caps), so the rise from vcc to vpp is too slow
> - load on any of the involved pins (esp. caps)
> - not tying LVP enable low
>
> When you want to use an RC-reset with ICSP split the R: Vcc - 10k - C -
> 22k - /MCLR with a diode over the 10k.

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2002\02\05@163231 by Byron A Jeff

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On Tue, Feb 05, 2002 at 02:58:44PM -0500, Kevin Olalde wrote:
> OK, thanks.  I've had a devil of a time getting consistent ISCP results, so
> along with excellent Wouter's suggestions below, are there more 'gotchas'?
>
> Did I read in a thread recently that a fast starting oscillator is also a
> potential problem?  Should I ground the OCS1 while programming?

Maybe. It's a risetime problem. You simply have to get MCLR from 0V to 13V
before the PIC starts executing the first instruction.

>
> I'm guessing I don't need to tie LVP low if I'm using HVP, correct?

Depends on the version. Some early versions had problems with LVP even when
doing HVP programming.

>
> How about breadboards?  Since I'm just starting out, most of my work is done on
> these.  Since I've read here that they are 'big capacitors', is this also a
> source of problems?  Even if no other part of the circuit is connected to RB6
> and RB7.

Not sure. I usually wire wrap. But right now I have one of Wouter's Wloader
dongles on a breadboard. Works fine.

>
> Finally what about the programmer?  Once ISCP programmer I've tried works about
> 10% of the time, on 16F84A and 16F628 parts always in HVP mode.  I recently got
> a ICD, on the same breadboard, same MCLR > 10K R > VCC, it works 100% percent of
> the time on 16F87x parts.  Maybe the inconsistent programmer is getting bit by
> the oscillator issue (I'll go try that now)?

Possibly. I prefer bootloaders because you can always open up a serial
terminal and talk directly to the target. With 16F87X parts I only use a
programmer to download the bootloader.

If you get a minute you can try my trivial LPV programmer. I also worked out
an ICSP interface, but I haven't drawn and uploaded the schematic yet.

http://www.finitesite.com/d3jsys

BAJ
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2002\02\05@163447 by uter van ooijen & floortje hanneman

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> Did I read in a thread recently that a fast starting oscillator is also a
> potential problem?  Should I ground the OCS1 while programming?

That's the vcc to vpp rise: you can get away with a slow rise when it does
not 'span' more than X clock cycles.

> I'm guessing I don't need to tie LVP low if I'm using HVP, correct?

Might work, might not work. Better be safe than sorry.

> How about breadboards?  Since I'm just starting out, most of my work is
done on
> these.  Since I've read here that they are 'big capacitors', is this also
a
> source of problems?  Even if no other part of the circuit is connected to
RB6
> and RB7.

I never found that a problem. A few 10's of pf is not what I would call big.

> Finally what about the programmer?  Once ISCP programmer I've tried works
about
> 10% of the time, on 16F84A and 16F628 parts always in HVP mode.  I
recently got
> a ICD, on the same breadboard, same MCLR > 10K R > VCC, it works 100%
percent of
> the time on 16F87x parts.  Maybe the inconsistent programmer is getting
bit by
> the oscillator issue (I'll go try that now)?

could be.
Wouter van Ooijen

Van Ooijen Technische Informatica: http://www.voti.nl
Jal compiler for PIC uC's:  http://www.voti.nl/jal
PICs kopen? http://www.voti.nl/shop

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2002\02\05@170842 by Tony Nixon

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wouter van ooijen & floortje hanneman wrote:
>
> > Did I read in a thread recently that a fast starting oscillator is also a
> > potential problem?  Should I ground the OCS1 while programming?
>
> That's the vcc to vpp rise: you can get away with a slow rise when it does
> not 'span' more than X clock cycles.
>
> > I'm guessing I don't need to tie LVP low if I'm using HVP, correct?
>
> Might work, might not work. Better be safe than sorry.

That was the reason I put an open collector output on the Pocket
programmers ICSP port. It is pulled low whenever the device enters
program mode.

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Tony

mICros
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