mattschinkel wrote:
> What is the purpose of the VDD pin on the ICSP connector?

So the programmer can power the target and control its voltage.  In some
cases, so that the programmer knows the actual target voltage in cases where
it can't be controlled.

> Is it ok to directly connect this VDD to power supply 5v VDD?
>
> Is it ok to directly connect this VDD to power supply 3v VDD?

These are bad questions.

The answer depends on the PIC and what you're trying to do with it at the
time.  For example, it is not OK to connect Vdd of a 18J PIC to 5V, as of
course is clearly spelled out in the datasheet.  On the other hand, you
can't connect a 16F877 Vdd to 3V and expect to perform a bulk erase or run
it at 20MHz.

For a general overview of ICSP, see http://www.embedinc.com/picprg/icsp.htm.


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