Hi Ariel,

I guess as not all input needs pull-up, so you can use the port where you
have internal pull-up when needed and for other inputs can go to other
ports. And also you can choose other PIC that has more ports with pull-up,
like 18F4450 has the PORTD as well, 18F97j60 has (too) many...

But to answer to your question, I have no idea, probably it's not just that
FET, it's also the control registers and other stuff involved that they
could save. I mean for example for 18F4450 they use the PORTE<7> bit to
control pull-up on PORTD, so they were definitely out of space with the
control bits and had no better place to integrate this functionality. Ugly
enough.

Tamas


On Wed, May 14, 2008 at 7:15 PM, Ariel Rocholl <foros@arocholl.com> wrote:

> I wonder why weak pullups availability in PICs is more an exception
> than a rule. I could understand old models, say 16F84 not having them,
> but I am surprised why most of the PIC18F don't offer that option
> except in PORTB, and in many cases just as a port wide on/off option.
> Given the size a simple pullup requires in the PCB, I have a hard time
> trying to understand why a simple FET is a costly resource in the die
> for the Microchip engineers.
>
> Some modern 8 bit PICs such as 16F688 has individual pin selectable
> pullups, but again only for 1 port.
>
> To make it worse, AVR offers individual pin selectable pullups in all
> ports, at least in all 8 bits micros I played with.
>
> Does anyone have a clue?
>
> --
> Ariel Rocholl
> Madrid, Spain
> --
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