Searching \ for 'In Circuit Programming 16x84' in subject line. ()
Make payments with PayPal - it's fast, free and secure! Help us get a faster server
FAQ page: www.piclist.com/techref/microchip/devprogs.htm?key=programming
Search entire site for: 'In Circuit Programming 16x84'.

Truncated match.
PICList Thread
'In Circuit Programming 16x84'
1998\02\10@234336 by NCS Products

flavicon
face
>- Use a small diode  in addition to the usual  resistor between Vdd and
>MCLR/VPP

The usual resistor?  We're supposed to use a resistor between Vdd and MCLR?
I've been tying it high, when not worried about in-circuit-programming.

Regarding the diode between Vdd and MCLR, is it possible to skip that without
damaging the PIC whilest in-circuit-programming?  Its easier to just use a
resistor
(how about 4.7K)?

1998\02\11@124652 by lilel

flavicon
face
> >- Use a small diode  in addition to the usual  resistor between Vdd and
> >MCLR/VPP
>
> The usual resistor?  We're supposed to use a resistor between Vdd
> and MCLR? I've been tying it high, when not worried about
> in-circuit-programming.

Ouch! Me too.  In order to ISP the boards I am using now I'll have to
cut traces (boo!)
>
> Regarding the diode between Vdd and MCLR, is it possible to skip
> that without damaging the PIC whilest in-circuit-programming?  Its
> easier to just use a resistor (how about 4.7K)?

Probably depends on how meaty your progger power supply is.  The app
note on Power up considerations recommends less than 40K due to
leakage current.  4.7K should satisfy this.


Best Regards,

Lawrence Lile

1998\02\11@133511 by davewave

flavicon
face
NCS Products wrote:

> >- Use a small diode  in addition to the usual  resistor between Vdd and
> >MCLR/VPP
>
> The usual resistor?  We're supposed to use a resistor between Vdd and MCLR?
> I've been tying it high, when not worried about in-circuit-programming.

To be honest, I cannot remember if there is a compelling reason to have a
resistor between Vdd and MCLR. It sure is handy to be able to reset the PIC
without removing power.

> Regarding the diode between Vdd and MCLR, is it possible to skip that without
> damaging the PIC whilest in-circuit-programming?  Its easier to just use a
> resistor
> (how about 4.7K)?

Never tried that, but it should work. My only concern would be if current flow
through the resistor was more than the PIC draws. Then it depends on what type
of
voltage regulator powers Vdd. A zener would keep Vdd at 5V. Some 3-pin devices
would not.

With Vpp of 13V and Vdd of 5V, there would be 1.7mA current flow through that
resistor during programming. I would add a 2.4k resistor between 5V and ground
on
the programming fixture - to insure this current has somewhere to go if
everything else failed. It is tempting to assume the PIC draws at least 1.7 mA
from Vdd during programming. The datasheet does not specify a minimum supply
current, so that would be an improper assumption. I might give your idea a try.
Thanks!

Dave

1998\02\11@180336 by Mike Keitz

picon face
On Tue, 10 Feb 1998 23:10:53 -0500 NCS Products <spam_OUTncsTakeThisOuTspamWORLDNET.ATT.NET>
writes:
>>- Use a small diode  in addition to the usual  resistor between Vdd
>and
>>MCLR/VPP
>
>The usual resistor?  We're supposed to use a resistor between Vdd and
>MCLR?
>I've been tying it high, when not worried about
>in-circuit-programming.

This works just fine, if you're not in-circuit programming.  Having a
resistor is nice for some experimental circuits so you can jumper MCLR to
ground to reset the PIC without having to turn the power off.
>
>Regarding the diode between Vdd and MCLR, is it possible to skip that
>without
>damaging the PIC whilest in-circuit-programming?  Its easier to just
>use a
>resistor
>(how about 4.7K)?

The problem with just a resistor is that current will flow "back" through
the resistor when MCLR is raised to 13V for programming.  This can cause
Vdd to rise above 5V, and/or overload the programmer's Vpp source.  Using
a rather large resistor (100K or more) should minimize or eliminate these
problems, but may cause others.  With the diode solution, the diode goes
in series with the resistor with the anode at the Vdd end so it is
reverse biased when 13V is applied to MCLR for programming.

I think both a diode and resistor are required so the programmer can set
MCLR to 0V with Vdd at 5V as part of the programming sequence.  With just
a diode, it wouldn't be possible to set MCLR low.


_____________________________________________________________________
You don't need to buy Internet access to use free Internet e-mail.
Get completely free e-mail from Juno at http://www.juno.com
Or call Juno at (800) 654-JUNO [654-5866]

More... (looser matching)
- Last day of these posts
- In 1998 , 1999 only
- Today
- New search...