Output Control Signals - Tandy 6000 Service Manual

DIRECTION IN
This signal defines the d ire ctio n o f m o tio n o f the
re a d /w rite head w hen the Step line is pulsed. A n
open c irc u it o r lo g ica l false defines the d ire c tio n as
" o u t" . I f a pulse is applied to the Step line, the
re a d /w rite heads m ove away fro m the center o f the
disk. I f this line is true, the d ire ctio n is defined as
" in " , and the re a d /w rite heads m ove in to w a rd the
center o f the disk.
Seek C om plete m ust be true p rio r to changing
directions and the a p plicatio n o f a d d itio n a l step
pulses.
REDUCED WRITE CURRENT
T he Reduced W rite C u rren t in p u t line is te r­
m inated, b u t is n o t used in the T M 5 0 0 series drives.
T he m icroprocessor a u to m a tica lly switches w rite
current.
DRIVE SELECT 0 THROUGH DRIVE SELECT 3
These c o n tro l signals enable the selected d riv e ' s in ­
p u t receivers and o u tp u t drivers. W hen lo g ic a lly
false, the o u tp u t drivers are open circuits and the
in p u t receivers do n o t
presented to them .
Selecting the appropria te ju m p e r b lo ck a t W 9
th ro u g h W 12 determines w hich select lin e activates
the drive.
N O T E
O n ly one drive m ay be selected at a tim e.

OUTPUT CONTROL SIGNALS

T he o u tp u t c o n tro l signals are driven w ith an open
collector o u tp u t stage capable o f sinking a m ax­
im u m o f 40 m illiam peres in a true state, w ith a
m a xim um voltage o f 0.4 v o lt measured at the
drive r. W hen the lin e d river is in the false state, the
drive r transistor is o f f , and the collector c u to ff is a
m axim um o f 250 m icroam peres.
A ll J l o u tp u t lines are enabled b y the respective
D rive Select lines.
acknowledge signals
SEEK COMPLETE
The Seek Com plete signal goes true when the
re a d /w rite heads have settled on the fin a l tra ck at
the end o f a seek. Reading o r w ritin g should n o t be
attem pted when Seek C om plete is false.
Seek Com plete goes false:
1. W hen a re ca lib ra tio n sequence is in itia te d
• b y the m icroprocessor at pow er on because
the re a d /w rite heads are n o t over T ra ck 0.
2. 500 nanoseconds, m a xim u m , a fte r the tra il­
ing edge o f a step pulse o r a series o f step
pulses.
3. W hen pow er is m o m e n ta rily lost, Seek
C om plete is false when pow er is restored
and remains false
re calibration is com pleted.
TRACK 0
The T ra ck 0 signal indicates a true state o n ly when
the d rive ' s re a d /w rite heads are positioned at T ra ck
0, the outerm ost data tra ck.
FAULT
The F a u lt signal is used to indicate a c o n d itio n ex­
ists in the drive th a t co u ld cause im p ro p e r w ritin g
on the disk. W hen this lin e is true, fu rth e r w ritin g is
in h ib ite d , as are o th e r drive fu n ctio n s, u n til the
co n d itio n is corrected.
This c o n d itio n is caused b y either the + 1 2 v o lt o r
+ 5 v o lt supply d ro p p in g below the specified lim its ,
and on pow er up u n til a successful re ca lib ra tio n se­
quence is com pleted.
INDEX
T he Index signal is provided once each re v o lu tio n ,
16.7 milliseconds n o m in a l, to indicate the beginn­
ing o f the tra ck. N o rm a lly , this signal is false and
makes the tra n s itio n to tru e to indicate Index. O n ly
the tra n sitio n fro m lo g ica l false to logical true is
va lid .
u n til an autom atic