From: Alan Pearce <kiwiantipodean@googlemail.com>
To: Microcontroller discussion list - Public. <piclist@mit.edu>
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Date: Mon, 16 Nov 2020 06:44:53 -0800
Subject: Re: [PIC] An In-Circuit Serial Programmer application
Thread-Topic: [PIC] An In-Circuit Serial Programmer application
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> Your successful experience with using a single pull up resistor and
> dropping the diode and capacitor confirms my suspicion the old
> Guideline's mostly a historic artifact.

I wouldn't go as far as describing the guidelines as a historic
artifact. It is more a case that most of the new chips have a power up
timer, so having a time constant on the MCLR pin is not as important
now.

But it is still relevant to the 16F84 chip depicted in the schematic,
and any other chips that don't have a power on timer.

On Mon, 16 Nov 2020 at 14:23, Don Kuenz <mail@crcomp.net> wrote:
>
>
> Brent wrote:
>
> <snip>
>
> > IMHO the ICSP circuit can be simpler yet remain effective i many cases.=
... just a
> > single pull up resistor to VDD. Value of 10k works well for me, using I=
CD3 and
> > ICD4. The resistor must present not too great a load to the programmer =
during HV
> > programming mode, nor push up VDD appreciably. Conversely it must be lo=
w
>
> > P.S. - It also works well with a Bootloader.
> > use the ICSP interface to install the TinyBootloader or an equivalent w=
ith
> > the ICSP Dat and Clk lines set at the Rx and Tx lines and you have a ni=
ce
> > development device with Programming, Debugging and Communications all
> > achieved via a USB/Serial adapter - Great to hand out to students or us=
e
> > for casual experimenting as well as in target applications.
> > enough value to prevent unwanted MCLR pul downs by noise. A couple of b=
asic
> > tips: keep traces short around ICSP, and don't expose VDD to the outsid=
e world
> > where it can pick up noise. In most cases the RC reset circuit is no gr=
eat loss with
> > most PIC's having fairly decent internal power up & brownout reset gene=
rators that
> > can be enabled.
> >
> > Yes ~ a bootloader is indispensable once you have settled on a good one=
.. All going
> > well you then only need to use ICSP once... so isolation becomes less i=
mportant. I
> > prefer a bootloader that doesn't require a button press, DIP switch, or=
 jumper, to
> > initiate it... these are time consuming and annoying steps during devel=
opment
> > code/program/debug cycles (frequent for me), and a complication when do=
ing field
> > updates. Ideal: bootloader runs for a brief time at reset and invokes l=
oading if
> > detected else runs application, optionally add hardware reset capabilit=
y by using
> > e.g. the RTS line, and/or have the application code invoke the bootload=
er after
> > receiving a serial escape sequence (unless this presents an unacceptabl=
e security
> > risk).
> >
> > Nice work on the web page though, good circuit design/description. I sk=
ip read it
> > and only noticed a missing "be" in 4th pragraph "can not left unused".
>
> Your successful experience with using a single pull up resistor and
> dropping the diode and capacitor confirms my suspicion the old
> Guideline's mostly a historic artifact. This thread gives me plenty to
> think about.
>     The typo on the webpage's now corrected. My website attempts to
> follow an ARRL format with its projects. It's my goal to push my lab
> notes out to the web.
>
> Danke,
>
> --
> Don, KB7RPU, https://www.qsl.net/kb7rpu
> There was a young lady named Bright Whose speed was far faster than light=
;
> She set out one day In a relative way And returned on the previous night.
>
> --
> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
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