Zenith Z-100 Series, Руководство пользователя, Страница: 71 / 150

C OM M A N D P H I LOS O P H Y
T here a r e t w o l e v e l s or t y p e s o f c o m m a n d s a s s o c i a t e d w i t h
t his c o n t r o l l e r . T h e f i r s t l e v e l i s a d i r e c t c o m m a n d t h a t
i s ex e c u t e d i m m e d i a t e l y a n d i s w r i t t e n d i r e c t l y i n t o t h e
controller 's command
register.
T hi s f i r s t t y p e of c om m a n d
i s used t o i n v o k e t h e s e c o n d t y p e o f c o m m a n d . T h e se c o n d
type of command is the primary communication mode between
the c o n t r o l l e r a n d t h e op e r a t i n g s y s t e m . In t h i s m o d e ,
c omma nd s a r e p l a c e d i n a b u f f e r i n m e m o r y a n d t h e c o n t r o l l e r
i s then g i v e n a d i r e c t c o m m a n d t h a t t e l l s i t t o f e t c h t h e
c omma nd s f r o m t h e b u f f e r . It d o e s t h i s v i a T e m p o r a r y M a s t e r
A cces s ( T N A — a s k n o w n a s D i r e c t M e m o r y A c c e s s o r D N A ) w h i c h
a llow s i t t o b r i n g t h e c o m m a n d i n t o i t s i n t e r n a l c o m m a n d
b uff er . S t a t u s i s r e t u r n e d t h e s a m e w a y , v i a T M A , u p o n
c omman d c o m p l e t i o n . A n in t e r r u p t i s a l s o g e n e r a t e d u p o n
c omman d c o m p l e t i o n t o n o t i f y t h e h o s t p r o c e s s o r t h a t c o m m a n d
exec u t i o n i s d o n e .
V.
V I . D I S K F O R M A T
The format used for the rigid disk is eighteen sectors of
5 12 by te s e a c h . M F M e n c o d i n g i s u s e d . T h e a c t u a l t r a c k
l a y o u t i s :
Gapl 1 6 x 4 E
R epea t 1 8 t i m e s :
SYNC
I D
AN
CYL
HDSEC
ECC
Gap2
SYNC
I D
AM
DATA
ECC
Gap3
3 x 0 0
1 1 x 0 0
1 x A l (mi s s i ng c l oc k )
1 x F E
2 x c y l i n d e r n umb e r
1 x h e a d / s e c t o r n umb e r
4 x e r r o r c o r r e c t i n g c o d e
1 1 x 0 0
1 x A l (mi s s i ng c l oc k )
1 x FR
5 12 x X X ( us e r da t a )
4 x e r r o r c o r r e c t i ng c o d e
1 3 x 4 E
230 x 4E ( n om i n a l )
Gap4
T his f o r m a t a l l o w s f o r a s p e e d t o l e r a n c e o f + / - 2 . 2 1 %