Spectravideo MKI, Service – Technical Manual

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FD1 793 FLOPPY DISK CONTROLLER DESCRIPTION
The F lo ppy D isk Forma t t e r b l ock d i a g ram
( STM-003-C ) .
The p r i mary sec t i on s
i nc l ude t he pa ra l l e l pro c e s s or i n t er face and t h e F l oppy D i sk i n t e r f ace .
DATA S
H
I
FT
REGISTER - Th i s 8-b i t reg i s t e r as semb l es se r i a l data f rom
the Rea d Da t a inpu t ( RAW READ ) du r i ng Re a d ope ra t i ons and trans fers se r i a l data
to t he Wr i te Data ou t put du r ing Wr i te ope ra t i ons .
DATA REGISTER - Th i s 8-b i t re g i s t e r is us e d as a ho l d ing re g i s t e r du r ing D i s k
R e a d a n d Wri t e ope ra t i o n s . In D i s k Rea d ope ra t i ons the a s s emb l e d d a t a by te is
tra n s f e r re d in para l l e l to the Da t a Reg i s t e r f rom the Data Sh i f t Regi s t e r . I n
D i sk Wr i t e opera t ions i n f o rma t i on is t rans f e rre d in para l l e l f rom the D a t a
Reg i s t e r to t h e Da t a Sh i f t Reg i s t e r .
Whe n execut i ng the Seek command the Da t a Reg i s t e r ho l d s the addre s s of the
de s i re d Track pos i t i on . This reg i s t e r i s l oaded f rom the DAL and ga ted� onto
the DAL und er proce s sor contro l .
TRACK REGISTER
-
Th i s 8-b i t reg i s t e r ho l d s the track number o f the current
Rea d /Wr i t e h ead pos i t i on . It is incremented by one e very t i me t he head i s
s t ep p e d i n ( towards track 7 6 ) a n d decreme n t e d by one when t h e head i s stepped
out ( towards track
00 ) .
The c on t e n t s of t he reg i st e r a re compared with the
re c o r d e d track number in the ID f i e l d du ring disk Rea d , Wr i t e , and Ve r i fy
ope r a t i o ns . The Tr ack Reg i s t e r c an be l oaded f rom or t r ans f e rre d to the DAL .
Th i s Reg i s ter shou ld no t b e loaded whe n the device is bus y .
SECTOR REGISTER ( SR)
-
T h i s 8-b i t reg i s t e r ho lds t he a dd r e s s o f the d e s i re d
se c t or po s i t i on . The con t e n t s o f the reg i s t e r are compar e d with the recorded
sector numb er in the ID f i e l d du r ing d isk Read or Wr i te ope rat i ons . The S e c tor
Reg i s t e r contents can be loade d f rom or t rans fer re d to the DAL . Th i s reg i s t e r
shou l d not b e l oaded wh en t he devi ce is b us y .
COMMAND REGISTER ( CR)
-
Th i s 8-b i t reg i s t e r ho l d s the command pre s ent l y be i ng
execu te d . This reg i s t e r shou ld not be l oaded when the dev ice is b us y un less
the new connand is a force inte r r up t . The command re g i s t e r can be loa ded f rom
t he DAL , but not rea d on t o the
DAL .
STATUS REGISTER ( STR)
-
Th i s 8-b i t reg i s t e r ho l d s device S t a t u s informa t i on .
The mean ing of the S t a t us b i t s i s a func t i on of the t ype of command previous ly
exec ute d . This reg is ter can be rea d ont o the DAL , but not loaded f rom the DAL .
CRC LOGIC - This log ic i s use d to check or to gene ra te the 1 6-b it Cyc l ic
Re dundancy Check ( CRC ) .
the po lynom ia l is :
G ( x )
=
x16
+
x 12
+
x 5
+
1
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