PIC MCU and MCLR internal pull-up

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Hi

Some pic microcontrollers (in my case pic16LF1503) - when MCLR is enabled - have MCLR pin internally connected to Vdd through a weak pull-up. My question is: Does it mean that I do not have to use external pull-up resistor to tie up MCLR pin to Vdd? I've been searching for a definite answer but I haven't found any. Some people say that if there is an internal pull-up, there is no need to use an external pull-up resistor and the MCLR pin can be left floating. Some people also say that even if there is an internal pull-up, it is recommended to use an external pull-up resistor (and they don't exactly say why). Thank you for any suggestions.
 

Hi,

Prove it to yourself, if you have Mclre ON and leave Pin1 unconnected , the program may not run at all, or run on and off because that pin is floating.
For that reason you must tie Pin1 to Vdd either direct or via a resistor, typically 10k, which is often used with a cap in a reset switch situation.

I believe the weak internal pull up you refer to is used by the chip to tie its internal MCLRE cicuitry up to Vdd, when you have Mclre = OFF


Edit, should add that the cost of the parts for a diy one, plus postage , time and effort, it is far cheaper to buy a reliable ready made Pickit.
If the Microchip ones are too expensive, then consider a Sure Pk2 clone or similar on via ebay
 
Last edited:

Prove it to yourself
Click to expand...

I did. It works perfectly fine, no random resets etc.


I believe the weak internal pull up you refer to is used by the chip to tie its internal MCLRE cicuitry up to Vdd, when you have Mclre = OFF
Click to expand...

PIC16(L)F1503 data sheet (page 56 6.4.1 MCLR ENABLED) says:
When MCLR is enabled and the pin is held low, the
device is held in Reset. The MCLR pin is connected to
VDD through an internal weak pull-up
Click to expand...
 

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