NOTE
p atterns an d a d j u s t t h e W r i t e D a t a w a v e -
form. Alt h ough a value cannot be specified for
w rite p r e c ompensation, T a n do n s u g g ests a
value of 125 nanoseconds for systems using
M FM double density recording format .
T M 8 4 8 - 1 E
a n d T M 8 4 8 -2 E
drives include a microprocessor-
controlled buffered seek capa-
bility. The controller ma y i s sue
step pulses of one microsecond
m inimu m
w i d t h , a n d f i f t e e n
microseconds minimu m spacing
between trai l in g edges. Internal
drive electronics issue step com-
ma nd s a t a
r a te of three
milliseconds.
WRITE GATE
The drive electronics ignore step pulses when
one of five conditions exists:
W hen t h i s s i g n a l i s t r u e ( l o w ) , t h e w r i t e
e lectronics are prepared for w r i t i n g d at a a n d
the read electronics are disabled. This signal
turns on W r i t e C u r r ent i n t h e s elected Read/
Write head. Data is w r i t t e n u n der th e control
of the Composite Write Data and Side Select
input l i n es. When the W r it e Gate l ine is false
(high), all write electronics are disabled.
When a write protected diskette is installed in
a drive, the write electronics are disabled, irre-
spective of the state of the W r i t e Gate or Side
Select lines. Wit h t h e N P j u m p e r i n s t a l l ed, a
diskette cannot be write protected.
1. The Wr it e Gate is true (low).
2 . Th e D i r e c t io n S e l ect i s f a l s e ( h i g h ) ,
and the head is positioned at Track 0.
3. The drive is
not selected.
4. When trying to
seek beyond Track 76.
5. W hen the diskette lever is opened.
NOTE
C hanges of s t at e o f t h e W r i t e
G ate l i n e s h o ul d o c cu r b e f o r e
the first Wr it e Data pulse.
CO M P O S ITE WRITE DATA
IN USE
When the drive is selected, this in t er f ace lin e
p rovides the bit s er ial C omposite Wr it e D a t a
p ulses that control th e swit ching of th e W r i t e
Current i n t h e selected head. The wr i t e el ec-
t ronics must be conditioned for wr i t i n g by t h e
Write Enable line.
For each high-to-low transition on the Compos-
ite Write Data l i ne, a flux ch ange is produced
a t th e w r i t e h e a d g a p . T h i s c a u ses a fl u x
change to be recorded on the media.
When a double-frequency type encoding tech-
n ique is used in which data and clock form th e
c ombined W r i t e
D a t a s i g n a l , i t i s r e c o m -
mended that th e r epeti t ion of th e h i g h -to-low
transitions, while wr i t i n g all zeros, be equal to
t he nominal data r a te , ~ 0 . 1 percent, and th e
repetition of the high-to-low transiti ons, while
writing all ones, be equal to twice the nominal
data rate, ~ 0.1 percent.
Host controllers may implement wr it e precom-
pensation ci r c u it s t h a t r e c ognize w orst c a se
SIDE SELECT
WRITE CURRENT SWITCH
This strappable feature controls the lever lock
solenoid when the DL option is installed.
Normally, W r i t e C u r r ent s w i t c h in g i s a ccom-
p lished by t h e h o s t c o n t r o l l er. A t r u e ( l o w )
l evel on t h i s l i n e r e duces the W r i t e C u r r e n t .
U sing o p t i o n I C , t he dr i v e a u t o m a t i c a l l y
reduces Write Current at Track 43.
The Side Select i n t e r f ace li ne, avail able only
on Tandon's TM 848-2E, defines which side of
a two-sided d i sk ett e i s u s e d f o r r e a d in g o r
w riti ng . A n
o p e n c i r c u i t , f a l s e ( h i g h ) l e v e l
3-4
