Greetings,
I have a couple questions about the PIC16F877 and it's i/o ports. The
data book clearly states that porta has full output drivers, but what
bout the rest of the ports? Portb doesn't concern me as much, as I know
i'm using it as an input, but what bout portc, portd, and porte? From
the diagrams, it looks like portc has full output drivers. Portd and
porte look the same, but I'm not sure what they are. Do they just go
high when activated and HiZ when deactivated? I also seem to remember
something about open collector outputs...but of course as I am looking
in the book now i cannot find any mention of it :) I am also confused by
the Schmitt Trigger inputs. What makes them different than a regular
input? All I've been able to find is a casual mention somewhere that you
need to drive them with a higher voltage, but what does that mean?
Now for my (not really) OT stuff. I'm looking for suggestions on what to
use for a couple of chips. IF anyone is familiar with the LM4066, it's a
quad bilateral switch. Basically 4 normally open switches on a chip. Has
anyone ever heard of a normally closed one? I'm trying to design some
fail-safe into my project, if the power to the controller fails, the
switches will go closed. I could just use pullup resistors and drive
them active low, assuming I can do that on portc and portd (See question
above). If there is a chip that defaults to NC, that would be much
easier. Also, I'm looking for suggestions on a data latch chip. I know
how to construct a data latch out of discrete logic, but i need a whole
chip for each line I want latched. 8 lines = 8 chips, and if I want 3
different latch channels I end up with 24 chips just for latch! Is there
an 8 bit data latch on a chip? I just want something that has 8 input
pins, 8 output pins, and an enable pin. (I suppose power connection pins
too :)) Also I'd want to multiplex two or three of these on one 8 bit
i/o port. Is this even possible?

I know this is alot of questions! Thank you in advance for your help!

Josh Koffman
joshy@mb.sympatico.ca