Spectravideo MKI, Service – Technical Manual

Page: 127 / 134

P I N
NO .
P I N NAME
30 WRITE GATE
3 1 WRITE DATA
3 2 READY
33 WRITE FAULT
VFO ENABLE
34
. TRACK 00
3 5 INDEX PULSE
SYMBOL
WG
WD
READY
IP
4 . 94
FUNCT I ONS
Th is ou tput is ma de va l id be fore
wr i t ing is to be performe d on the
d i ske t t e .
A 2 50 ns ( MFM ) or 500 ns
( FM)
p u l se
per i t s trans i t i on . WD con t a i ns the
un i que Add r e s s ma rks as we l l as data
and c l ock in bo th FM and MFM forma t s .
Th i s input indicates d i sk rea d l i ne s s
and i s samp l e d for a logic h igh
be fore Read or Wr i te commands are
pe r forme d . If Ready is l ow the Read
or Wr i te ope rat ion i s not performed
and an inte rrup t i s gene r a t e d . Type
I opera t ions a re performed regard l e s s
of the s t a t e of Rea dy . The Rea dy'
input appea rs in i nve rted format a s
S ta t u s Reg i s t e r b id 7 .
Th i s is a b id i rect i ona l s igna l use d to
s ign i fy wr i t ing fa u l t s at the dr i ve ,
and to enab l e the externa l PLD data
s e pa r a t o r . When WG
=
1 , P in 33
func t i ons a s a VFOE outpu t . VFOE w i l l
g o low du r ing a read ope rat i on a f t e r
the hea d ha s loaded and se t t led ( HLT
=
1 ) . On t he 1 79 5 / 7 , i t w i l l rema in l ow
unt i l the l a s t b i t o f the second CRC
byte in t he ID f ie l d . VFOE w i l l then
go h igh un t i l
8
bytes (MFM ) or
4
bytes
( FM )
be fore the Address Mark . It w i l l
then g o act ive un t i l the last b it o f
the second CRC byte o f the Data F ie l d .
On
the 1 79 1 /3 , VFOE w i l l rema in l ow
unt i l the end o f the Data F i e l d .
Th is input informs the FD 1 79X tha t the
Read/Wr i te head is pos i t i oned over
Track 00 .
Th i s input info rms the FD 1 79X when the
index hole is encounte red on the
d i sket te .