Floppy D I S K Interface - Spectravideo SVI 318 Service – Technical Manual

Du ri ng D i r e c t Memo r y Acc e s s ( DMA ) t ype s o f d a t a trans f e r s be tween the D a t a
Reg i s t e r of t he FD 1 79X a n d t he p roc e s so r , t he D a t a Re que s t ( DRQ ) ou t p u t i s u s e d
in Da t a T ra n s f e r c o n t ro l .
and Wr i t e ope r a t ions ,
On D i s k R e a d o p e r a t ions the Da t a R e qu e s t i s ac t i va t e d ( s e t h igh ) when an
a s s e mb l e d s e r i a l input b y t e is t ra n s f e r r e d i n p a r a l l e l t o the D a t a R e g i s t e r .
Th is b i t i s c l e a r e d whe n the D a t a Reg i s t e r i s re a dy by the p roce s s o r .
Da ta Reg i s t e r is. read a f t e r o ne or more cha rac t e rs a r e l o s t , by h a v i ng new d a t a
t r a n s f e r r e d i n t o the reg i s t e r p r i o r t o p ro c e s s o r re a dou t , t h e Lo s t D a t a b i t i s
s e t i n t he S t a t us R eg i s t e r .
se c t o r i s re a che d .
On D i s k Wr i t e ope ra t ions the d a t a R e qu e s t i s ac t i va t e d when the Da t a R e g i s t e r
t r a ns f e rs i t s cont e n t s t o t he D a t a S h i f t Reg i s t e r , and r e qu i r e s a new d a t a
I t i s re s e t whe n the Da t a Reg i s t e r is l o a d e d w i t h new data by the
b y t e .
p r oce s s o r . I f new da ta i s n o t l oa d e d at t he t i me t he next s e r i a l by t e i s
re qu i re d by the F loppy D i s k , a b y t e o f z e r o e s i s wri t t e n o n t h e d i s k e t t e a n d
t he Lo s t Da t a b i t i s s e t in t he S t a t us Reg i s t e r .
A t t h e comp l e t i o n o f every conunand an INTRQ i s g en e ra t e d .
e i t h e r r e a d ing t he s t a t u s reg i s t e r o r by l oa d ing the command reg i s t e r with a
ne w conunand . In a dd i t i o n , I NTRQ i s gene r a t e d i f a Forc e i n t e r r up t comma n d
c ond i t i on is m e t .

FLOPPY D I S K INTERFACE

The 1 79 3 ha s two mod e s of ope r a t ion ac c o r d i ng to t h e s t a t e of DDEN ( P i n
When D DEN 1 , s ing l e d e n s i t y i s s e l ec te d .
=
24 ) 2
is a t MHz .
is s e t a t 1 MHz for bo t h s ing l e d e n s i t y and doub l e d en s i t y .
a t 2 MHz , t h e s t ep p ing ra t e s o f
e qu a l s 1 MHz the s e t imes
D I S K READ OPERAT IONS
S e c t o r l e ng t h s o f
f o rma t s . F or FM , DDEN
sh ou l d be p l ace d to a logic a l
t i me by a special by te
f i e l d i s zero , t h e n the s e c t o r
02 , 5 1 2 bytes .
then
o f s e c t o r s pe r t rack a s far a s t h e FD1 79 is conce rned
s e c t o rs .
Th e numbe r
255 t r ack s . For IBM 3 740 compa t i b i l i t y , sector lengths
s e c t o r s p e r t rack .
by te s / se c t or with 2 6 sec tors / t rack ; or lengths
sectors / t rack. ( See Sector Length Tab l e )
Th i s s i gna l a l s o app e a r s as s t a tus b i t 1 dur ing R e a d
T he R e a d ope r a t i on cont i nu e s unt i l the e n d o f
when
Howev e r , in t e r f ac i ng w i th t h e m in i - f l oppy , t h e CLK
3 , 6 , 1 0 ,
a re doub l e d .
1 28 , 256 , 5 1 2 o r
shou ld be p laced to log i cal " 1 " �
"0" .
in t he " I D"
l ength
03 , then
I f t he s e c t o r l eng th i s 1 0 2 4 b y t e s .
o f t rack s as far a s
For Sy s t em 34 compa t i b i l ity ( MFM ) , sec
I n e i t her
and 1 5 ms are ob t a i na b l e .
1 024 are ob ta inab l e in
Sec tor lengths are
f ie ld . I f t h i s S e c t or l ength by t e in the I D
1 28
i s b y te s .
t h e FD1 79 is
o f 1024
4 . 83
INTRQ i s re s e t by
ca s e , the CLK i np u t ( P i n
When the
Whe n CLK
e i t h e r FM ro MFM
For MFM f o rma t s , DDEN
de t e rm in e d at forma t
2 5 6
I f 0 1 then b y t e s .
The numb e r
c a n b e f rom 1 t o
conce rne d i s f rom 0
a re 1 2 8 b y t e s with 26
t or l eng ths
b y te s / se c t o r with
I f the
3 7 ) .
input
c lock is
I f
2 5 5
to
are 2 56
8