I'd like to use the internal pull-up features on 16X84
for RB4-7 inputs.
I have cleared the RBPU in the OptionRegister, enable
interupts upon RB change.
But, while testing my application, I notice that something
was wrong. Just by approaching my finger around the PIC
chip without touching it, my program was detecting some RB change
conditions!
When measuring the RB7-4 pin voltage, I notice that it was 0V as if the
pull ups were not activated.
As a work-around, I have pulled up the 4 pins using 18K external
resistors
and problems disapeared?
I would like to understand the data sheet picture representing the RB4-7
ports
concerning the week pull-up activation :
TRISB is and-ed with /RBPU and the result is complemented.
In my configuration, it makes 1 and /0=1 => 0 driving the (MOS?)
transistor.
Does it mean that the RBx pin is no more connected to the Vhigh source?
Is it why I have notice 0v on RBx pins after enabling the pull up?
What does microchip mean by weak pull-up? I thought it was as if an
external high-value resistor was connected between the pin and Vhigh,
but my mind now gets really confused.

Thanks for your help,

Benoit CELLE