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M od e l
536 3 8
S e rv i c e
8-4 6 .
I t s h o u l d be n oted t h a t o n e c a n e a si l y c o n ve rt f ro m t h e s y m b o l o g y of p o s i t i ve - l o g i c
m e re l y b y s u b st i t u t i n g a p o l a ri t y i n d i c a t o r ' � f o r e a c h n e g a t i ve i n d i c a t o r · 0 w h i l e l ea vi n g
t h e d i s t i n c t i ve s h a pes a l o n e . To c o n v e rt f r o m t h e s y m b o l o g y o f n e g at i ve-l og i c , a p o l a ri ty
L::: :. . i s s u b st i t uted f o r eac h n e g a t i o n i n d i c a t o r 0 , a n d t h e
i n d i c a t o r
f o r the A N D s h a pe o r v i c e ve rsa .
8-4 7 .
I t was s h o w n t h a t a n y d e vi c e t h a t c a n p e rf o r m
a n d v i c e ve rsa . D e M o rg a n 's t ra n sf o r m a t i o n i s i l l u s t rated i n E xa m p l e s
the t r a n sf o r m at i o n a re :
At e a c h i n p u t or o u t p u t h a v i n g a n e g a t i o n , 0 , o r p o l a ri t y , � . i n d i c a t o r , d e l ete t h e
1 .
i n d i c a t o r .
A t e a c h i n p u t a n d o u t p u t n o t h a vi n g a n i n d i c a t o r , a d d a n e g a t i o n · 0 , o r p ol a ri t y � .
2 .
i n d i ca t o r .
S u b st i t ute t h e A N D s y m b o l ·
3 .
do
not a l t e r t h e a ss u m e d c o n v e n t i o n ; pos i t i ve - l og i c stays p o s i t i ve , n e g a t i ve-l o g i c
stays n e g a t i ve , a n d m i xe d - l o g i c stays m i xed .
8-4 8 .
T h e c h o i ce of s y m b o l m a y b e i n f l u e n ce d b y t h ese c o n s i d e ra t i o n s: . 1 · T h e o pe rat i o n
b e i n g p e rf o r m e d m a y best b e u n d e rstood a s A N
b a s i c g a t e , t h e i n p u ts wi l l u s u sa l l y be c o n s i d e red a s i n h e re n t l y a c t i ve h i g h o r a c t i ve l o w
, e . g . , t h e J a n d K i n p u ts of a J - K f l i p -f l o p a re act i ve h i g h a n d a c t i ve l o w , r e s pe c t i ve l y , .
c h a i n of l o g i c , u n d e rsta n d i n g a n d t h e w ri t i n g of l o g i c e q u a t i o n s a re often fa c i l i tated i f a c t i ve
l o w o r n e g a te d o u t p u t s feed i n to a c t i ve l o w o r neg ated i n p u t s .
O
t h e r S y m b o l s
8-49.
M o re s y m b o l s a re req u i red to d e p i c t c o m p l e x l o g i c d i a g ra m s . S o m e of t h e o t h e r
8-50.
sym b o l s a re a s f o l l o ws :
-C>
I
I
8 - 1 0
0
D y n a m i c i n p u t acti vated by t ra n s i t i o n f ro m a l o w level to a h i g h l e ve l . T h e
o p posite t ra n s i t i o n has n o effect at t h e o u t p u t .
D y n a m i c i n p u t acti vated b y t ra n s i t i o n from a h i g h level to a l o w leve l . T h e
o pposite t ra n s i t i on has n o efect at t h e o ut p ut.
Exc l u s i ve OR f u n ct i o n . T h e output w i l l ass u m e its i n d icated acti ve l evel if
and o n l y if o n e and o n l y o n e of t h e i n puts ass u me s its i n d icated acti ve l e ve l .
I n ve rt i n g f u ncti o n . T h e o ut p u t is l ow if t h e i n pu t i s h i g h a n d i t i s h i g h if t h e
i n pu t i s l o w . The t w o symbols s h o w n a re e q u i va le n t .
N o n i n v e rti n g f u ncti o n . The o u t p u t i s h i g h i f the i n pu t i s h i g h a n d i t i s l o w i f
t h e i n p u t i s l o w . T h e two symbols s h o w n a re e q u i va le n t.
l o g i c c a n a l so p e rf o r m A N D l o g i c
O R
. fo r t h e
D ,
s y m b o l .
O R
i
o r
2
•
I n a f u n c t i o n m o re c o m p l e x t h a n a
D
O R .
s h a pe i s s u b st i t uted
O R
1
t h ro u g h 7 . T h e r u l e s of
o r v i c e ve rs a . T h ese steps
, 3 ,
I n a
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