12F675 and GP3 as Input

[Frank607]

I have a problem with a PIC 12F675 and a switch on GP3. I have made a simple test program that will one time blink a LED after a switch is pushed.
This program only works (run one time) when the Pickit 2 is connected. If I disconnect the Pickit 2 the program runs nonstop and regardless of the switch.

I have placed the program in this message and post some screenshots from the schematic.

Thanks for helping me out.

[medelec35]

Hi Frank,
I'm a bit confused looking at your circuits.
You have got 10K from MCLR to GND
But you have also got 10K+ 470R going from MCLR to + 5V
This means that no mater if switch is pressed or not, the resistors will act as a potential divider and bias VPP at:
10k/(10k + 470R +10k) * 5V
= 2.44V
That's classed as logic 1
So when switch is pressed & released, Voltage on VPP is going from 5 back down to 2.44V

Just remove R17 and R18.


Martin

[Frank607]

Thanks Martin,

It is working now. I have used this ICSP config with the resistors in all my schematics because this is the “standard” from the ICSP / Pickit datasheets.

But I never used this on a MCLR pin in combination with a switch due to the maximum pins on this chip.

Indeed, this was my error.

Thanks also for the good explanation. It's now clear to me.

[medelec35]

Hi Frank,
Your welcome.
Glad to have been some help.


Martin