Post by thread:Best pullup resistor value for /MCLR pin?

Hi! What would be the best pullup resistor value to connect +5V to the /MCLR to achieve the most stable operation? (I'm using PIC18F452) I've seen circuit diagrams with straight 5 volts, some with really high resistors, and this given 'ICD ready' circuit with 47K Ohm... Regards, Jean-Pierre -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

> What would be the best pullup resistor value to connect +5V > to the /MCLR to achieve the most stable operation? (I'm > using PIC18F452) > > I've seen circuit diagrams with straight 5 volts, some with > really high resistors, and this given 'ICD ready' circuit > with 47K Ohm... Unless you are in a very (elctromagnetically) noisy environment it does not matter much, that's why you see such a wide range used in practice. You can determine the maximum value from the /MCLR pin current and required voltage, it used to be ~ 50k on older PICs, IIRC it is much higher now. For ICSP the programmer will specify the minum value, for my Wisp628 the recommended value is 33k. Note that if you also put a capacitor on the /MCLR things will be different: there must be some resistance between the cap and the /MCLR pin (see uChip datasheets), and for ICSP that resistor must probably have the 'recommended' value. A combination of ICSP and an external brown-out reset chip complicates the matter even further.... Wouter van Ooijen -- ------------------------------------------- Van Ooijen Technische Informatica: http://www.voti.nl consultancy, development, PICmicro products -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

On Wed, 10 Dec 2003 10:14:35 -0500, you wrote: >Hi! > >What would be the best pullup resistor value to connect +5V to the /MCLR to achieve the most stable operation? (I'm >using PIC18F452) > >I've seen circuit diagrams with straight 5 volts, some with really high resistors, and this given 'ICD ready' circuit >with 47K Ohm... > >Regards, > Jean-Pierre It is not hugely critical - there is no 'best value'. If you want to do in-circuit programming, you need to ensure that the resistance is high enough not to upset your programmer. Anything from 0 to 100K would probably fine for most applications. Higher values will increase noise pickup, so I'd suggest a maximum of 10K unless there is also a cap to ground. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.