I just wonder if it's always necessary for me to put a diode in between of the reset switch and the MCLR pin of a PIC? My reset circuit for PIC is by connecting a 33K resistor in series with a 0.1uF capacitor whereby one end of resistor is connected to the Vout of 7805 and one end of the capacitor is connected to ground. The reset switch is connected in parallel to the capacitor and the cathode of diode is connected to the end of reset switch which is not connected to ground but connected to the resistor and capacitor.
My problem is that this reset circuit works fine for PIC16F877 but when I change my PIC to PIC18F452, it doesnt work properly. If I bypass the diode by short-circuiting it, I can reset my PIC18F452, otherwise, I cant reset it at all.
He means R but you should be careful with the values of R if you use a CCS ICD. I recommend a value of 22 K to 47 K in this case and you can also not use the diode because programming voltage (13V) is applied via the reset pin when ICSP programming.
Those circuits seem mainly for solving special situations, and stand a good chance of making things worse.
I have always just run a 10k resistor from MCLR to Vdd and I've never had a problem... at least not one I'm aware of being related to the MCLR circuit, it would be quite inaccurate to say I've never had a problem without being more specific.
I've never even used a reset button. Seems to work fine.
To solve this problem and forget about it you should use proper reset IC such as MAX1232. It has Res-L, Res-H and SW input and you can select voltage threshold and reset time.
I just dont trust this resistor/cap combination, and it doesn't matter wheather this is PIC, 8051, ...... it always works.