Spectravideo MKI, Сервисное – Техническое руководство

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For
r ea d ope r a t i o n s , t he FD 17 93 re q u i r e s RAW READ
D a ta ( P in
2 7 ) s ig na l
wh i c h
i s
a 2 5 0 ns
pu l s e pe r f l ux t r ans i t i on and
a
R e a d
c l ock
( RCLK )
s igna l
t o ind i c a t e
f l ux t ra n s i t i on
s p a c ing s .
T h e
RCLK
( P in
2 6 )
s ig n a l
i s
p ro v i d e d b y
some d r i ve s
b
u t
i f no t
i t ma y
be d e r ive d e x t e rna l l y by
Pha s e lock l oop s ,
o
n
e
sho t s , or
c o
unt
e r t e c h n i qu e s . In a d d i t i on ,
a
Read G a t e S
ig
n a
l
is
p rov i de d as an ou tput
( P in
2 5 ) wh i c h
c a n be u s e d to i n f o rm pha s e l o c k
l oops
whe n
to
a
c q
u
i
re
s y n c h r o n i z a t i on . Wh en r e a d ing
f rom
t he me d i a
i n
FM ,
RG i s
ma d e
true when
2
b y t e s
o f
z
e
r o e
s
a r e d e t e c t e d . The FD1793
mus t
f i n d an a dd r e s s
ma rk w i t h i n the
ne xt 10 by t e s ; o
t
h
e
rw
i s
e R G i s r e s e t a n d t he
s e a rch for 2
b y t e s of z eroe s
be g in s
a l l o v e r aga i n .
I f
a n a d d re s s ma rk
i s
found w i t h i n 1 0
b y t e s ,
RG
rema i n s
t r
u
e
a s l ong
as t h e
FD 1 7 93 i s d e r i v i ng any
u s e f u l
i n forma
t i o
n
f rom t he d a t a
s t r e am .
S im i l a r l y for
MFM , RG
i s m a d
e
ac t i ve whe n 4 b y t e s o f "00" o r
"FF"
a re
d e t e c te d . T he FD f 7 93
m u s t f ind an a ddre ss mark w i t h in t he nex t 1 6 bytes ,
o t h e r w i s e
RG
i s re s e t a
n d s e
a
r
c
h
r
e s u
m
e
s
.
Du r i ng re a d ope ra t i ons
( WG
=
0 ) , the
VFOE
( P in 33 ) i s prov i d e d for pha s e l ock
l o op
s y n c h ro n i z a t i on . VFOE
w i l l
go
ac t i ve whe n :
( a )
Bot h
HLT and
HLD a r e T r ue
( b )
S e
t
t in
g
Time , if
p rogramme d ,
has exp i re d
( c )
th e
1793
i s insp e c t i ng d a t a of f the d i sk
I f
WF /VFOE
i s no t u s e d , l eave op e n or t i e to a l OK res i s t o r to +5 .
D I S K WR ITE OPERAT ION
Whe n wr i t i ng i s
t o
t a k e
p l a ce on
the
d i sk e t t e
the W r i t e Ga t e
( WG )
ou tpu t i s
a
c
t
i
v
a
t
e
d ,
a l low ing cu r r e n t t o
f l ow i n to t he Read/ Wh i t e
h ea d .
As a preca u t i on
t
o e r roneous w r i t i ng the f i r s t d a t a b y t e mus t b e l o a d e d i n t o
the Data Reg i s t e r
i n r e s p o n se
t o
a Da t a R e que s t
f rom the
FD1 7 9 3
b
e f
o
re
the
Wr i t e G a te s ignal can
be a c t i va t e d .
W r i t ing
i
s
i nh i b i te d wh en
t
he
Wr i te
P
r
ot
e c
t
in put i s a
log ic
low, i n wh ich c a s e
an y
Wr i t e
command
i s
i
mme
di a
t
e l
y
t e rm i na t e d , a n i n t e rrupt i s g
e
n e
r
a t e d a n d t he
W
r
i
t e P ro t e c t
s t a t us b i t i s s e t .
The
Wr i t e Fa u l t inpu t , wh en a c t i va t e d ,
s
i
g
n
i
f
i
e s
a
wr i t i ng fau l t
cond i t i o n
de t e c t e d
i n d i sk dr ive e l ec t r o n i c s such as
f
a
i
l
u
r
e
to
d e t e ct wr i t e cu rre nt f low when the Wr i t e G a t e i s a c t i va t e d . On
d e t e c t i on of th i s f au l t t he FD1 7 93 t e rm i n a t e s t he cu rrent command , and s e t s the
Wri t e
Fa u l t
bit ( b i t 5) in the S ta t u s Wor d . The Wr i t e Fa u l t i np u t shou l d be
ma d e
i na c t i ve wh en t he
Wr i te Ga t e ou tput b ecomes inact i ve .
For w r i t e ope r a t i o ns , the
FD1793
p rovides Wr i t e G a t e ( P i n 3 0 ) and Wr i t e Da t e
( Pin
3 1 )
ou t p u t s . Wr i t e d a t a cons i s t s o f a se r i e s o f 500 ns pu l s e s in
FM
( D DEN
=
1 ) and 2 50 ns p u l s e s i n MFM ( DDEN
=
0). Wr i te D a ta p rovides the u n i que
a dd re s s ma rks in bo th forma t s .
4 . 84