Quick Question About sharing programming pins on a PIC

[2camjohn]

Is it good practice to use the PGC and PGD pins to switch MOSFETs while also using them to reprogram the microcontroller?


In other words, can I still use pins RB6 and RB7 to program my PIC while they are connected to the gate of a MOSFET (and 680k pull down)?

At the time of programming there will be no current for the mosfets to sink.




Is that a good idea?

Cheers
John

 

[geko]

There's no reason not to use those pins for both ICSP and normal functions.

You just need to ensure that the whatever they connect to won't take the ICSP signals out of spec' for programming. From what you describe I would think your application will be okay.

There is a Microchip appnote that talks about this https://ww1.microchip.com/downloads/en/DeviceDoc/30277d.pdf

 

[Nigel Goodwin]

Even easier than that - and with no restrictions - you need a socket to plug your ICSP lead in to, so simply give that socket two rows, and plug a dummy plug in that joins the pins across to the required I/O circuit. To program, unplug the link plug (disconnecting the pins entirely), and plug the programmer in - no restrictions, dead easy!.

 

[geko]

Given the OPs application that wouldn't make it easier since the ICSP programmer should have no problem with the MOSFETs on RB6/7.

It would also likely make a PCB layout more complex. The easiest way is design the application circuit to work with the ICSP if at all possible.

 

[kchriste]

In other words, can I still use pins RB6 and RB7 to program my PIC while they are connected to the gate of a MOSFET (and 680k pull down)?

Should work fine as long as the ICSP also uses pull down resistors (The ICD2 does) and that the loads on the MOSFETs don't mind being toggled during the ICSP process.