Hi, don't know if this will help anyone, but on the main
tech.microchip forum I saw a few people asking about using
a picstart plus (PSP) to give in-circuit programming (ICSP)
of applications using flash chips like 16F84 ad 16F877 etc.

With the help of two guys that posted there who had done it
before I was able to get it happening pretty easy, and thought
I might post details here for reference of anyone (especially
newbies to ICSP) who might want to do this at some point.

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How to use Picstart Plus to do ICSP (on 16F84)
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Firstly I made a simple header. This is a long-legged 18pin
socket to go into the PSP, with four wires soldered to it.

Here are the wires:

* Gnd (Vss) -----       ground wire
* MCLR      --R--       470 ohm series resistor
* RB7       --R--       470 ohm series resistor
* RB6       --R--       470 ohm series resistor

These connect to the same PIC pins on the app, in my case
I designed the app board with the 470 ohm resistors on the
board and a nice plug for the ICSP.

Important, I used no capacitors on the app on the MCLR
pin. I just used a 68,000 ohm resistor to hold the MCLR
high to 5v when in normal operating mode. This is very simple,
and has low parts cost.

To program the app, I simply connected power to it (via
a on/off switch) from my regular power source not from
the PSP. The PSP does NOT power the amp or the pic when
programming in this circuit. I connected the ground from
the PSP to the ground of the app's power supply of course.

One the app was powered, the PSP holds the app in reset
mode as it holds the MCLR pin at 0v. Then I used MPLAB
as normal to program or read the 16F84 in the app. This
works as normal, like when programming a 16F84 in the
socket of the PSP.

When programming is complete I can just switch the app
power off, unplug the programming plug, and switch the
app power back on to run the app as normal. Quick and easy!

Just a couple of notes, app's that use a "reset" chip on
the MCLR line may need to make some changes to ensure that
the PSP can draw the MCLR line to 13v very quickly to
ensure good programming. Also my app used the RB7 and RB6
as inputs, so also using these for the ICSP gave no problems.
I tested adding 10k resistors to both these pins to 0v,
and tested again with the 10k resistors to 5v. Both cases the
ICSP still worked fine. I would guess that means that you
don't need to "buffer" these pins but simply use a 10k
resistor to your circuit and you can still use them as inputs.

I have programmed the thing with a number of 16F84 chips,
and programmed it a couple of hundred times with NO program
or read failures (unless I forget to switch the app on
before programming!).

I know this is a long letter and I apologise to the PIC
experts who probably know all of this, just seen a few
newbies ask about ICSP lately and not everyone has the
budget or desire to spend big bucks on ICSP.
YES, you CAN do ICSP with a picstart plus.

Roman

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