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LOGIC CON VENTIONS
The d i s k d r i v e u s e s s t a n d a rd 5 - v o l t T T L l o g i c , w h e r e a v o l t a g e m o r e p o s i t i v e than
+2. 4 v o l t s ( t u r n - o n t h r e s h o l d ) is c o n s i d e r e d a l o g i c a l o n e (high), and a v o l t a g e m o r e
n e g a t i v e than +0. 4 v o l t s ( t u r n - o f f t h r e s h o l d ) is c o n s i d e r e d a l o g i c a l z e r o (low).
I n t e r f a c e s i g n a l l o g i c l e v e l s a r e i n v e r t e d by line r e c e i v e r s and li ne d r i v e r s f o r u s e
by the d i s k d r i v e and the c o n t r o l l e r , r e s p e c t i v e l y .
v o l t a g e m o r e p o s i t i v e than +2. 4 v o l t s ( t u r n - o f f t h r e s h o l d ) is c o n s i d e r e d a l o g i c a l
z e r o , and a v o l t a g e m o r e n e g a t i v e than +0. 4 v o l t s ( t u r n - o n t h r e s h o l d ) is c o n s i d e r e d
a l o g i c a l on e ( s e e F i g u r e 3 - 7 ) .
The l o g i c s y m b o l o g y u s e d in the d i s k d r i v e is s h o w n in F i g u r e 3 -8 .
is d e s c r i b e d and all c o n d i t i o n s a r e d efi n ed .
D E T A I L E D LOGIC D E S C R I P T I O N
The d e t a i l e d l o g i c d e s c r i p t i o n is d iv id e d into t h r e e m a j o r fu nct ion s:
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Cont ro l L o g i c
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R e a d / W r i t e Head P o s i t i o n i n g L o g i c
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R e a d / W r i t e L o g i c
C ON T R O L LOGIC
The c o n t r o l l o g i c co n t ai n ed in the d i s k d r i v e p e r f o r m s t h r e e p r i m e fu n cti on s:
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A c c e p t s c o n t r o l l e r S E L E C T c o m m a n d and e n a b l e s all i n t e r f a c e l o g i c
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D e t e c t s and p r o v i d e s index and o p t io n al s e c t o r p u l s e s
F i g u r e 3 - 7 .
I n t e r f a c e L o g i c L e v e l s
3 - 1 0
F o r all i n t e r f a c e s i g n a l s , a
E a c h e l e m e n t
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