Quote Originally Posted by sougata View Post
Hi,

While using as MCLR the weak pull-up is enabled. Thus you do not need an external resistor from VDD to the MCLR pin. Still you could use the MCLR to keep the MCU in reset using external circuitry by pulling it down.

When you use the pin as I/O the POR is completely internal and the chip is automatically reset on powerup. This time the weak pull-up associated with the MCLR is detached. So if using as an input and needs to be pulled up you have to use an external pull-up resistor.

Hope this helps.
Crystal clear. Thank you very much.