pin voltage while programming

[ruijc]

Greetings,

This may be a silly question, but this has been on my mind for some time now.

I've noticed that if i connect some leds to any pic pins, during programming some of them blink.

My doubt is:

I have some projects where my pic's source is 3V and i have connected 3V components to it's I/Os ( sensors, displays ).
I can isolate the pic's VDD with a jumper for the programmer and have the PGD and PGC dedicated for programming. The problem is the voltage generated on the other pins when programming because the programming voltage is higher than 3V.

Can the 3V components be damaged while programming the Pic?
Is there a solution for these cases?

Thanks

[mister_e]

Depends how you design your thing. On most sensitive programmer, you can set the target Vdd voltage, that solve the problem, if any. An home made LDO for Vdd and resistor divider for PGC/PGD? could be this too. Never tried it though.

You can Isolate your PIC from the "external world" with jumpers and diode, that's for sure, but first, check what happen on I/O while programming. I doubt you'll see 5 Volts peaks, more likely some spurious volts.

Another thing... does this board will require some firmware update? Case not, you could just solder the pic on, program it, then populate the other components.

[mackrackit]

I isolate VPP and VDD, never worried about PGD and PGC. But I never thought about it either...

[ruijc]

Hi guys,

Thank you for your thoughts,

Actually i can isolate both VDD, PGD, PGC and VPP either using jumpers or using these pins only for ICSP.

The problem are the other pins. I'm not being able to accurately measure the voltage peeks but there's definitely voltage in those pins ( not all of them though ).

If one of them peeks more than 3V i may damage the component.

Regards
Rui

[mister_e]

Isolate Vdd and Vss then.... or, like I said, use a programmer allowing to modify it's Vdd... OR modify it yourself, not that hard.