I heard that Pickit's LPC board can be modified with another chip (instead of PIC16F690) to allow debugging without the use of any 'ICE header' etc junk solutions. Does anyone know anything about it ?

Also it puzzles me why designers of LPC board used RA3 port instead of other free pin (eg. RA5) for SW1 (it causes all kind of problems).

 

I heard that Pickit's LPC board can be modified with another chip (instead of PIC16F690) to allow debugging without the use of any 'ICE header' etc junk solutions. Does anyone know anything about it ?

Not specifically but if you do a parametric search on 16F and 18F families from http://www.microchip.com/pagehandler/en-us/family/8bit/ selecting 20pin DIP package you'll get a list of parts that likely have the same pinout. I did a cursory look but all the ones I saw indeed required a header for debugging. Perhaps others don't but you can find out in the Development Tool Selector.

Microchip's stated reason for requiring the header is that on parts intended for high volume/minimum cost, they can provide more functionality in place of the internal debug hardware for the same cost. A 4K 18F with a full set of peripherals for about a buck is the result. An additional benefit is that the headers don't require resources or I/O pins from the eventual target PIC as do chips with internal debugging capability. On very small parts, this is a valuable feature.

Who knows why RA3 is used like they did. Maybe to demonstrate how to share the ICSP pins with other I/O but that's why I keep my Dremel tool handy.

At any rate, the functions on the LPC board don't look like they would be hard to replicate on a breadboard. I frequently develop on more capable chips with the same basic memory and IO maps, avoiding resources not present on the eventual target chip. Works well.

Good luck!