W01791 - Floppy Olek Controller
IC
The W01791 is an MOS
LSI
device which perfarms
tha
functions
01
a Floppy Disk formaUcontroller
in
a single-chip
Implementation.
The
W01791 cantains
aH
Ihe features
01
its predecessor,
the
1771, plus
the
added leatures necessary
to
read,
write
and
lormat a double-denslty dlskelte. These include: address mark
detecllon,
FM
and
MFM
encode
and
decode
lagie,
window
extension
and
write precompensalion.
WD1791 OrgenlZllUon
The Floppy
oisk
Formaller black diagram
Is
iIIustraled ln
Figure
2.
The primary seclions include Ihe parallel Processor
Interface
and
the Floppy olsk interface.
Oeta
Shlft Reglster - This eight,bil resister assembles seriai
data Irom the Read Data input (RAW
REAO)
du
ring
Read
operations
and
transI
ers
seriai data la
the
Write
Data
output
during Wrile operations.
-1
""
1
.,
_
....
"
.......
,~ ..
·,,·oo
-
...
•
•
•
•
Oeta
Reglet.r
- This eight-bil register
15
used
as
a holding
reglster during Oisk
Read
and
Wrile operations.
In
Disk
Rud
operations, the assembled data byte
Is
transrerred
in
paraUelto
the
Data Register Irom
the
Data Shift Aegister.
In
Disk Write
operations, inlormation
is
translerred
in
parallel Iram
the
Data
Reglster
to
the
Data Shift Register. When executing the
Seek
command,
the
Data Reglsler halds the address
01
tha desir9d
track position. This register can
be
Ioaded
rrom
the
OAl
and
gated onlo the
DAl
under processor control.
Treck
Regleter
- This eight·bit regisler
ho
Ids the track
number
01
the
current
Read/Wrila
head
position. It is
Incremented
by
one every lime
the
head
Is
steppe<!
in
(towards
Track
76)
and
decremented
by
one
when
the head
is
stepp:!d
ouI (Iawards Track 0). The contents
01
the register are
compared
with the record track number
in
the
ID
field duri1g
disk
Read,
Write
and
Verily operations. The Track Regis'er
can
be
Ioaded
Irom or translerrad
ta
the
oAl.
This
Regis'
er
should not
be
loaded when the
FOC
is
busy.
Sector
Regleter
(SR) - This eighl-bit register holds
Ile
address of the desired seclor position. The contents
01
11e
reglster
are
compared with the recorded seclor number
in
Ile
-l
LJ
'---------
..
'
•
'
..
-
•
•
-
-
..
,.,.",.
'00'-
.".
-
•
.
_,
....
-,
..
.'
Figure
2.
WD1791 Black
Dlegr.m
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