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L
D E
Se l ec t o r c o n t ro l b l o c k . T h ese s y m b o l s a re used w i t h a s a rray of O R s y m b o l s
so
to p r o v i d e a p O i n t o f p l ac e me n t f o r se l e c t i o n I S · o r g a t i n g ' G , l i ne s . T h e
S l
s e l e c t i o n l i n e s e na b l e t h e i n p u t d e s i g n a ted
m ea n s of a b i na r y c o d e w h e r e S O i s t h e l e a st s i g n i f i c a n t d ig i t . I f t h e 1 l e v e l o f
t hese l i n e s i s l ow, p o l a ri ty i n d i ca t o r s I b,. , w i l l b e u sed . T h e g a t i n g l i ne s h a ve
SE L
a n A N D re l a t i o n w i t h the respe c t i ve i n p u t of e a c h O R f u n c t i o n : G 1 w i t h t h e
G 1
G 2
i n p uts n u m be red 1 , G 2 w i t h t h e i n p u t s n u m b e red 2 , a n d s o fo r t h . I f t h e
(J 3
e na b l i n g l e ve l s of t hese l i ne s i s l o w , p o l a r i t y i n d i ca t o r s b,. , w i l l be used .
C o m pl e x L o g i c Devices
8 - 5 5 .
8-56.
L o g i c e l e m e n t s can be c o m b i ned to p r od uce very c o m p l e x d e v i c e s t h at can pe rf o r m
m o re d i ff i c u l t f u n c t i o n s . A c o n t ro l b l o c k s y m b o l c a n be u sed to s i m p l i f y u n d e rsta n d i n g o f
m a n y c o m p l e x d ev i c e s . Seve ra l e xa m p l es of c o m p l e x d e v i c e s a re g i ven h e re .
> 1
S e l e c t o r c o n t ro l b l o c k used t o s i m p l i f y A N D p o rt i o n of a q u a d A N D - O R
s e l e c t g ate . W h e n G 1 i s h i g h , t h e d a t a presented a t t h e " 1 " i n p u t s w i l l b e
;;, 1
g a ted t h ro u g h . W h e n G 2 i s h i g h , t h e d ata p resented at t h e
1
g a ted t h ro u g h .
2
1
> 1
2
R eg i ste r c o n t ro l b l o c k used t o i l l u st rate a q ua d D-type l a tc h . T h e re i s a
c o m m o n a c t i ve l ow reset ( R " a n d a c o m m o n e d g e t r i g g e re d c o n t ro l i n p u t
I
I .
S i nc e t h e re i s o n l y o n e d e p e n d e n c y r e l at i o ns h i p , t h e c o n t ro l l i n g i n p u t
C
i s n o t n u m be red a n d t h e c o n t ro l led f u nc t i o n s
S h i f t reg i st e r c o n t ro l b l o c k used to s h o w c o m m o n i n p u t s t o a b i d i re ct i o n a l
s h i f t reg i ste r . N o t i c e t h a t " - m " m e a n s s h i ft t h e c o n te n ts to t h e l ef t o r u p b y
" m " u n it s . N ote: i f m = 1 , i t m a y b e o m i tted . I n p u t s " a " a n d " b " a re e a c h s i n g l e
d
p i n s t h a t h a ve t w o f u n c t i o n s . I n p ut " a " e n a b l es o n e of t h e i n p u ts to t h e
I C
3D
t o p D-type f l i p -f l o p , 1 D , a n d a l so s h i fts t h e reg i st e r c o n t e n t s d ow n o n e
1 0
u n i t . I n p u t
C 1 .2 . 3
3 D
a l so s h i fts t h e reg i ste r c o n te n t s u p o n e u n i t . l n p u t "c " l oad s a l l f o u r f l i p -f l o p s
F F
l
C 1 .2. 3
i n p a ra l l e l , 3 D . I n p u t " d " i s a c o m m o n reset. T h e o ut p u t d e l a y i n d ic a t o r i s
3 D
F F
l
u sed b e c a u s e t h e se a re m a ste r-s l a ve f l i p -f l o ps .
C 1 .2.3
3 D
2 0
FF
e n a b l e s o n e o f t h e i n p u t s to t h e b ot t o m f l i p -f l o p , 2 D , a n d
"
b
"
0 ,
1 , . . . . n e a c h O R f u nc t i o n b y
" 2 "
i n p u t s w i l l b e
I
D , a re s u b sc ri pted w i th a
M o d e l 5 3 6 3 8
S e rv i c e
C .
8 - 1 3
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