"Paul B. Webster VK2BZC" wrote:
> 
> Tony Nixon wrote:
> 
> > >From the data book....
> > Port latch = 1 and TRISB = 1 enables weak pullup if RBPU = 0
> 
> > You mention that your port latch = 0.
> 
>   Sorry Tony, wrong data book!  You are referring to AVR devices, we're
> talking PICs.  Weak pull-up is enabled when RBPU is low and individual
> TRIS line is high.  The port latch status is irrelevant.
> 
>   James, the port B pullups are in the order of 100k; for IÓC you need
> 4k7.  Use resistors.
> --
>   Cheers,
>         Paul B.

Hi Paul,

I'm sorry, I've never seen an AVR data book :-)

The PIC data book that I have (1994 pg 2-557) states.....

RPBU = 0: PortB pull-ups are enabled by individual latch values.
(From OPTION Register text)

Port latch = 1 and TRISB = 1 enables weak pullup if RBPU = 0
(From PortB Block diagrams)

But......

Looking at the simplified schematic of PortB pins, there is no
connection from the Port Latch to the pullups control.

There seems to be a contradiction here.

Furthermore, Port latch AND tris values are said to affect only RB<7:4>
while the tris by itself affects only RB<3:0>.



-- 
Best regards

Tony

http://www.picnpoke.com
mailto:sales@picnpoke.com