strange MCLR Pin problem 12F629

[Erik]

I use the GP3 PIN (MCLR) as input of a higher than 5V voltage square wave (i call it Vdd2). Unfortunately my program works fine till the square wave voltage (Vdd2) is below 9V, but if the voltage gets higher the chip doesn´t seem to work anymore - that means it outputs a square wave with the same frequency like the input on Pins which i have internally pulled up (and that should not be...).

MCLR-reset is disabled.

I use a 50 kOhm pull-up (to Vdd2) on GP3 und a standard 7805 for power supply (which is powered by Vdd2).

Does anyone have an idea what´s going wrong ?!?
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This message was ported from CCS's old forum
Original Post ID: 144515324

[chas]

:=
:=I use the GP3 PIN (MCLR) as input of a higher than 5V voltage square wave (i call it Vdd2). Unfortunately my program works fine till the square wave voltage (Vdd2) is below 9V, but if the voltage gets higher the chip doesn´t seem to work anymore - that means it outputs a square wave with the same frequency like the input on Pins which i have internally pulled up (and that should not be...).
:=
:=MCLR-reset is disabled.
:=
:=I use a 50 kOhm pull-up (to Vdd2) on GP3 und a standard 7805 for power supply (which is powered by Vdd2).
:=
:=Does anyone have an idea what´s going wrong ?!?

Whether or not MCLR is set to an input, it is always the high voltage programming pin. The max input voltage for the MCLR pin when it's an input is Vdd. I would suggest that when that pin goes above 9V in your circuit, it is setting the processor into program mode. If you truly need to have a high voltage for that signal, I would suggest a series resistor and a diode clamp to Vdd. Hope this helps.
___________________________
This message was ported from CCS's old forum
Original Post ID: 144515325