17 Jun
2011
17 Jun
'11
12:21 p.m.
On Fri, Jun 17, 2011 at 1:08 PM, Chuck Guzis <cclist at sydex.com> wrote:
On 17 Jun 2011 at 2:41, Dan Roganti wrote:
yes but in essence these are still only positive logic designs, only the
assertion levels(active state) of a signal changes, it still relies on
Pos.Voltage = Logic Hi.
Positive Logic Design vs. Negative Logic
Design
Most moderately complex designs contain a mixture of both. What irks me when reading a schematic is the idiot who
assumes that a 7400
is
ALWAYS represented as a quad NAND gate.
It depends on what the assertion levels(active states) are for the inputs in
the design. If the assertion levels are logic Lo, then it would be better to
view this using the negative logic symbol as a bubble input OR gate then.
I hope you don't expect all databooks past & present to be revised :) These
were always written in the context of positive logic.
This sort of thinking, while
being bush-league, also obfuscates the actual circuit
design.
Negative logic design is usually not for the faint hearted ;)
=Dan