Reusing PGC & PGD pins

[Demon]

Do I have special considerations to take when I reuse ICSP pins?

Do I need a jumper during programming if I have a device connected, like a resistor/LED?

(I couldn't find any REUSE PGC/PGD/ICSP posts)


EDIT: I have found this post elsewhere that says we can do it (I'm using it as a heartbeat LED to diagnose any timing issues).

https://forum.microchip.com/s/topic/...NnAEAW/t321516

[tumbleweed]

Yes you can reuse them but you need to be careful as to what circuitry you hang off the pins.

Most ICSP programmers have 4.7K pull-down resistors on the PGC/PGD pins and assume the pins will idle low.
You shouldn't put too much additional load on the pins, add pullups or capacitors, or use the pins as inputs if they'll be actively driven high/low by the connected circuitry.

[Jerson]

I connect the ICSP port on the PCB to the ICSP pins of the controller directly. The Pins in turn go to the rest of your circuitry via resistors so that you do not need programming jumpers to perform ICSP. The resistors help resolving contention. Hope this helps.

[richard]

i like to connect some critical or dangerous hardware to one of those pins, like the enable pin for the high power laser or the step input for the Z axis.
that way you really know when reprograming is happening

[Demon]

To be clear, I will NOT have the circuit powered when I'm programming. The PCB must be removed from the main board in order to be programmed (I use the same connector for operation and for programming).

Specifically, now I'd like to connect the output of a 74HC14 on PGC or PGD (running out of pins).

[Demon]

i like to connect some critical or dangerous hardware to one of those pins, like the enable pin for the high power laser or the step input for the Z axis.
that way you really know when reprograming is happening

Pics or it didn't happen.

[richard]

its very easy to do.
on a pic curiosity board the pins are just there begging you to use them. you can kinda forget the programmer is on board
when there is no need to plug and unplug it at all.

[tumbleweed]

To be clear, I will NOT have the circuit powered when I'm programming. The PCB must be removed from the main board in order to be programmed (I use the same connector for operation and for programming).

Specifically, now I'd like to connect the output of a 74HC14 on PGC or PGD

I wouldn't do that. Your safest bet would be to have a jumper you can remove to isolate the output of the HC14 from the PGC/PGD pin while you're programming.

[pedja089]

I conect ICSP directly to pins. And from konektor, other part of circuit connect via 2K resistor. If you use pin as inputs, then other hardver driving state of pin. So not to have colision with programmer, put some resistors.
For MCLR use 10K resistor. As it can reach 13V. I generaly avoid using MCLR.
But this makes it hard to use debuger....

[tumbleweed]

And from konektor, other part of circuit connect via 2K resistor.

You have to be careful when using the pin as an input.

While a series R can help isolate the pin from the ICSP programmer, if the external circuit is driving the pin high then this can change the idle state of the pin that the PIC sees during programming from low to high depending on the R value. The ICSP typically has 4.7K pulldowns on the PGC/PGD pins, so the series R creates a voltage divider which you may need to take into account too.