Tandy 2000 Service Manual page 628

intel
82724
PRELINfl[NARV
Symbol
Pln
No.
Type
Connec-
tlon
To
Name
and
Functlon
RESET
1
I
pP
Reset: Places FDC
in
idle state.
Resets
out-
put
lines
to
FDD
to
"0"
(low). Does not clear the
last
specify command.
RD
2
1l
t
I
pP Read:
Control
signal
for transfer
of data
f
rom
FDC
to
Data Bus. when
,'0"
(low).
WR
3
;I
t
)
pP
Write: Control
srgnal
for
transfer
of
data
to
FDC via Data Bus. when
0'
(low)
CS
A
a+
pP
Chip
Select:
lC selected
when'0'(loy).allow-
Ing RD and WR
to
be
en ab
led
Ao
q li'
pP
Data/Status
Register
Select:
Se
lect
s
Dat
a
Reg (Ap
Reg
(Au =
0)
contents
to
be sent
to
Data Bus.
DBo
-DB,
6--13
lot
1l
LtP
Data Bus: Brdirectional
B-Bit Data
Bus.
DRQ 14
o
DMA
Data DMA
Request:
DMA Reqruest
is
berng
rnade
by
FDC
when
DRQ
1 ''
DACK 15
DMA
DM
A
Acknowledge:
DMA cycle
is
actrve
when 0" (low)
and
Controller rs
perform-
rng
DMA transf er.
TC
16
DMA
Terminal Count:
Indi-
cates the termrnatron of
a
DMA
transfer
wl-ren
1
'
(high)t2r
IDX
17
FDD
Index: Indicates
the
beginning
of a
drsk
track
INT
1B
o
pP
Interrupt: Interrupt
Re-
quest Generated
by
FDC
CLK
1a
Clock: Srngle
Phase
B
MHz {4 MHz
for
nrini
floppies)
Squarewave
Clock
GND
2C
Ground: D.C.
Power
Ret
u
rn
Note
tr
Drsabled
when
CS
1
Note
2
TC nrust be aetrvaled
to
terrnrnate
the
Exer-utLcn Phase
of any'rjcltrlnlantl
Table
1.
Pin Description
Symbol
Pln
No. Type
Connec-
tlon
To
Name
and
Functlon
vcc
40 D.C.
Power: +5V
RWISEEK
39
o
FDD
Read
Wrlte
/ SEEK:
When ri1'r (high)
Seek
mode selected
and
when "0" (low)
Read/
Write
mode
selected.
LCTI DIR 38
o
FDD
Low
CurrenUDirection:
Lowe
rs
Write
cu
rrent
on inner tracks
in
Read/Write mode,
cie-
termines direction
head
will step in
Seek mode.
FR
STP 37
o
FDD
Fault
Reset/Step:
Re-
sets
fault
FF
in
FDD
in
Read/Write
mode, pro-
vides
step pulses
to
move head
to
another
cylinder in
Seek
mode.
HDL 36
o
FDD
Head Load:
Comnrand
which
causes read/write
head
in
FDD
to
contact
d
iskette.
RDY
35
I
FDD
Ready:
lndicates
FDD
is
ready
to
send
or
re-
ceive
data. Must
be tied
h
ig
h
(g
ated
by
t
he
I
ndex
pulse)
for mini fleppies
wh lc
h do not
normaily
!91"
g
n9"9y
1'
Write
Protect
I
Two-
Side: Senses Write
Prc.r-
tect status in
Readi'
Write
mode.
and
Two
Side
Med
ia in
Seek
mode"
WP TS 34 FDD
FLT
TRKO
33
I
FDD
Fault/Track
0:
Senses
FDD
fault ccndition
in
ReadrWrite
mode
and
Track
0 condition
in
Seek mode.
PSr,PSo
31 ,32
o
FDD
Precompensation (pre-
shift): Write
precom-
penSation status dt
rirrg
MFM mode. Determirres
early, late, and
norrrial
trmes.
WR DAIA
30
o
FDt)
Write Data:
Serial
c
jock
and data bits
to
FDD
DS,
,DSN
28.29
o
FDD
Drive
Select
:
Se
le
c
ts
FDD
unit
HDSEL 27
o
FDD
Head
Select:
Hea'J
1
selected
when '
1
(high)
Head
0
selecteC
when
,'0"
(low).
6-225
AFN-01259C