Subject: Digital circuit notation conventions

From: Brian Chase <[email-masked]>
Date: Fri Jun 13 11:12:02 2003

I figure this is at least somewhat on topic.  I've been reading through
_The Art of Digital Design_ by Prosser and Winkel [1] to with the
intention of building the PDP-8/I clone project outlined in the book.
I skipped ahead to the meaty chapters outlining the design of the
system; I found myself pleasantly surprised.  I can say that I've a
reasonable understanding of how it all works.  I can certainly
understand the fascination people have with the "8"; it's not that hard
at all to wrap one's brain around it.

Having satisified myself that I'm up to the task, I've now moved to
reading the initial chapters so I'll understand the basics.  There are a
few rough spots where I feel the authors impatiently gloss over some of
the topics.  And then there's one section in the second chapter where
they basically deride "postive logic" and "negative logic" notation
conventions as evil while promoting what they claim to be their own
"mixed logic" convention.

Methought they protested /a bit/ too much, and not being familiar with
what it proper or put into practive, I pulled out Horowitz and Hill [2]
to see what they had to say.  From what I can tell, they seem to be
advocates of "assertion-level logic" notation--which looks to be the
same as Prosser and Winkel's mixed logic.  What I'm wondering is whether
mixed logic and assertion-level logic notations are in fact the same,
and then which notation convention(s) are most commonly found in
practice.

It was only a decade ago that I had my intro to digital logic design
lectures and labs, but I don't remember there being any discussion of
different notation conventions.  Then again, it's possible that ten
years worth of software knowledge has squeezed out what hardware bits
we covered.

-brian.

[1] The Art of Digital Electronics: An Introduction to Top-Down Design,
    2nd Ed, Franklin P. Prosser and David E. Winkel, Prentice Hall,
    1987.

[2] The Art of Electronics, 2nd Ed., Paul Horowitz and Winfield Hill,
    Cambridge University Press, 1989.