Tandy 6000 HD, Service Manual

Page: 276 / 416

N O T E
T M 8 4 8 - I E a n d T M 8 4 8 - 2 E
d r iv e s in c lu d e a m ic ro p ro c e s s o r-
c o n t r o l l e d
b u f f e r e d s e e k
c a p a b ilit y . T h e c o n tr o lle r m a y
is s u e s te p p u ls e s o f one m ic ro s e ­
c o n d m in im u m w id t h , a n d f i f ­
te e n m ic ro s e c o n d s m in im u m
s p a c in g b e tw e e n t r a i l i n g edges.
I n t e r n a l d r iv e e le c tro n ic s is s u e
s te p c o m m a n d s a t a r a t e o f
th r e e m illis e c o n d s .
Th*) d r iv e e le c tro n ic s ig n o re s te p p u ls e s w h e n
one o f f iv e c o n d itio n s e x is ts :
1. T h e W r it e G a te is tr u e (lo w ).
2. T h e D ir e c tio n S e le c t is fa ls e ( h ig h ) ,
a n d th e h e a d is p o s itio n e d a t T r a c k 0.
3. T h e d r iv e is n o t se le cte d .
4. W h e n t r y i n g to seek b e y o n d T r a c k 76.
5. W h e n th e d is k e tte le v e r is opened.
COMPOSITE WRITE DATA
W h e n th e d r iv e is s e le c te d , t h is in t e r f a c e lin e
p ro v id e s th e b i t s e r ia l C o m p o s ite W r it e D a ta
p u ls e s t h a t c o n tr o l th e s w itc h in g o f th e W r it e
C u r r e n t i n th e s e le c te d head. T h e w r it e
e le c tro n ic s m u s t be c o n d itio n e d f o r w r i t i n g b y
th e W r it e E n a b le lin e .
F o r e a c h h ig h - to - lo w t r a n s it io n o n th e C o m p o s­
i t e W r it e D a ta lin e , a f l u x c h a n g e is p ro d u c e d
a t th e w r it e h e a d gap. T h is causes a f l u x
c h a n g e to be re c o rd e d on th e m e d ia .
W h e n a s in g le - d e n s ity (F M ) ty p e e n c o d in g
te c h n iq u e is u se d i n w h ic h d a ta a n d c lo c k
fo r m th e c o m b in e d W r it e D a ta S ig n a l, i t is
re c o m m e n d e d t h a t th e r e p e t it io n o f th e h ig h -
to -lo w tr a n s itio n s , w h ile w r i t i n g a l l zeros, be
e q u a l to o n e - h a lf th e m a x im u m d a ta r a te , 2 5 0
k ilo h e r t z ± 0 . 1 p e rc e n t. T h e r e p e t it io n o f th e
h ig h - to - lo w tr a n s it io n s w h ile w r i t i n g a l l ones
s h o u ld be e q u a l t o th e m a x im u m d a ta r a te ,
500 k ilo h e r t z ± 0 . 1 p e rc e n t.
H o s t c o n tr o lle r s m a y im p le m e n t w r it e p re c o m ­
p e n s a tio n c ir c u it s t h a t re c o g n iz e w o r s t case
p a tte r n s a n d a d ju s t th e W r it e D a ta w a v e ­
fo r m . A lt h o u g h a v a lu e c a n n o t be s p e c ifie d f o r
w r it e p re c o m p e n s a tio n , T a n d o n s u g g e s ts a
v a lu e o f 125 n a n o se co n d s f o r s y s te m s u s in g
M F M d o u b le d e n s ity r e c o r d in g fo r m a t.
WRITE GATE
W h e n t h is s ig n a l is tr u e (lo w ), th e w r it e
e le c tro n ic s a re p re p a re d f o r w r i t i n g d a ta a n d
th e re a d e le c tro n ic s a re d is a b le d . T h is s ig n a l
t u r n s o n W r it e C u r r e n t i n th e s e le c te d R e a d /
W r it e h e a d . D a ta is w r it t e n u n d e r th e c o n tr o l
o f th e C o m p o s ite W r it e D a ta a n d S id e S e le c t
in p u t lin e s . W h e n th e W r it e G a te lin e is fa ls e
(h ig h ) , a l l w r it e e le c tro n ic s a re d is a b le d .
W h e n a w r it e p ro te c te d d is k e tte is in s t a lle d in
a d r iv e , th e w r it e e le c tro n ic s a re d is a b le d , i r ­
re s p e c tiv e o f th e s ta te o f th e W r it e G a te o r
S id e S e le c t lin e s . W it h th e N P ju m p e r
in s ta lle d , a d is k e tte c a n n o t be w r it e p ro te c te d .
N O T E
C h a n g e s o f s ta te o f th e W r it e
G a te lin e s h o u ld o c c u r b e fo re
th e f i r s t W r it e D a ta p u ls e .
IN USE
T h is s tra p p a b le fe a tu r e c o n tro ls th e le v e r lo c k
s o le n o id w h e n th e D L o p tio n is in s ta lle d .
WRITE CURRENT SWITCH
N o r m a lly , W r it e C u r r e n t s w itc h in g is a c c o m ­
p lis h e d b y th e h o s t c o n tr o lle r . A t r u e (lo w )
le v e l o n t h is lin e re d u c e s th e W r it e C u r r e n t.
U s in g o p tio n IC , th e d r iv e a u t o m a t ic a lly
re d u c e s W r it e C u r r e n t a t T r a c k 43.
SIDE SELECT
T h e S id e S e le c t in t e r f a c e lin e , a v a ila b le o n ly
o n T a n d o n ’s T M 8 4 8 -2 E , d e fin e s w h ic h s id e o f
a tw o -s id e d d is k e tte is u se d f o r r e a d in g o r
w r it in g . A n o p e n c ir c u it , fa ls e (h ig h ) le v e l
3-4