Du ri ng D i rect Memory Acc e s s ( DMA ) t ype s o f data trans fers be tween the Data
Reg i s t e r of t he FD 1 79X and t he p roce s so r , t he Data Re que st ( DRQ ) ou tput i s used
in Dat a Tra n s f e r contro l . Th i s s i gna l a l s o appears as sta tus bit 1 dur ing Read
and Wr i te ope r a t ions ,
On D i s k Read operat ions the Da t a Reques t is ac t ivat e d ( se t h igh ) when an
a s s e mb l e d s e r i a l input byte is t ra n s f e rred in para l l e l to the Data Reg i s t e r .
Th is b i t i s c l e a r e d whe n the Data Reg i s t e r i s re a dy by the p roce ssor .
I f the
Da ta Reg i s t e r is. read a f t e r o ne or more cha rac t e rs are l o s t , by having new d a t a
trans f e r r e d into the reg i s t e r p r i o r t o p roce ssor rea dou t , t h e Los t D a t a b i t i s
s e t in t he S t a tus Reg i s t e r . T he R e a d ope r a t i on cont i nues unt i l the e n d o f
se c t o r is re ache d .
On D i s k Wr i t e ope ra t ions the data Requ e s t i s ac t i va t e d when the Da t a Regi s t e r
t rans 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 requi res a new d a t a
byte .
I t is re set whe n the Dat a Reg i s t e r is loaded with new data by the
p roce s so r .
I f new da ta i s n o t l oaded at t he t i me the next s e r i a l by te is
re qu i re d by the F loppy D i s k , a byte of zeroes is wri t t e n on the disk e t t e and
t he Lo st Da t a b i t i s s e t in t he S t a tus Reg i s t e r .
A t t h e comp l e t io n o f every conunand an INTRQ i s genera t e d . INTRQ is res e t by
e i ther r e a d ing t he s t a t us reg i s t e r or by l oa d ing the command reg i s ter with a
new conunand .
In a dd i t i on , INTRQ i s gene r a t e d i f a Force inte rrup t comma n d
c ond i t i on is met .
FLOPPY DISK INTERFACE
The 1 79 3 ha s two modes of ope rat ion ac cording to the s t a t e of DDEN ( P in
3 7 ) .
When D DEN
=
1 , s ing le dens i t y i s se l ec te d . In
e i t her
ca se , the CLK i nput ( P in
24 )
is a t
2
MHz . Howeve r ,
when
in t e r fac ing with the m in i - f l oppy , the CLK
input
is s e t a t
1
MHz for bo th s ing l e dens ity and doub l e d en s i t y . When the
c lock is
a t
2
MHz , the s t ep p ing ra t e s o f
3 , 6 , 1 0 ,
and 1 5 ms are ob t a i nab l e . Whe n CLK
e qua l s
1
MHz the se t imes
a re
doub l e d .
DISK READ OPERAT IONS
Sector l e ngths of
1 28 , 256 , 5 1 2
or
1 024 are ob ta inab l e in
e i ther FM ro MFM
forma ts . For FM , DDEN
shou ld be p laced to log i cal " 1 " �
For MFM forma t s , DDEN
shou l d be
p l aced to a logical
"0" .
Sec tor lengths are
de t e rm ined
at forma t
t i me by a
special by te
in
t he
" ID"
f ie ld .
I f this S e c t or l ength by te in the I D
f i e l d is zero , then the sector
l ength
is
1 28
byte s .
I f 0 1 then
2 5 6
byte s .
I f
02 ,
then
5 1 2 bytes .
I f
03 , then
t he s e ctor l eng th i s 1 024 bytes . The number
o f s e c t ors pe r
t rack as far as the FD1 79 is conce rned
can be f rom
1
to
255
s e c t o rs . Th
e numbe r
of
track s as far as
the
FD1 79 is
conce rned i s f rom
0
to
255
track s .
For
IBM
3 740 compa t i b i l i t y , sector lengths
a re 128 bytes
with 26
s e c t o rs per
t rack . For Sy stem 34 compa t i b i l ity
( MFM ) ,
sec
t or l eng ths
are 2 56
by te s / sector with 2 6 sectors / t rack ; or lengths
of
1024
byte s / sector
with
8
sectors / t rack. ( See Sector Length Tab l e )
4 . 83
Содержание MKI
Страница 1: ...SERVICE TECHNICAL MANUAL VOL 1 l SVI318 328 MKI MKII COMPUTER SYSTEM SVI SPECTRAVIDEO ...
Страница 7: ...4 Remove the seven retaining screens 5 Remove the cover 2 2 ...
Страница 8: ...6 Remove the screens on the metal cover 7 Remove the metal cover 2 3 ...
Страница 9: ...To r e assemble u se the above procedures in the rever se order 2 4 ...
Страница 134: ...5 CIRCUIT SCHEMATIC AND COMPONENT LAYOUT 5 1 ...