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