PORTB: internal pull-up : pull-up resistor size

Christophe · Joined: 10 May 2005 Posts: 323 Location: Belgium

Hi,

I just wanted to know what is the size of the internal pull-up resistors of portB? Using a PIC16F886.

regards

Ttelmah · Guest

They are not really 'resistors'. They are MOSFETs, wired to act as current sources. As such, they behave differently to resistors. With a resistor the current drawn increases as the load voltage goes down (so more current is drawn with a connection to '0v', than with a connection to (say) '3v'). The current sources give nearly the same current drawn in both cases.
The currents are significantly 'variable', ranging from about 50uA, to 400uA.
The data sheet for the 886, only gives the figure for the PORTA weak pull up (on MCLR), but the PORTB ones are the same. If you think of them as perhaps equivalent to a resistor of about 50000R, they should pull up at least this well, and in most cases 'better'.

Best Wishes