Tandon TM848-1E Specification And User Manual page 19

NOTE
T M 8 4 8 - 1 E a n d
drives include a microprocessor-
controlled buffered seek capa-
bility. The controller may 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 minimum spacing
between trail ing edges. Internal
drive electronics issue step com-
mands at a
milliseconds.
The drive electronics ignore step pulses when
one of five conditions exists:
1. The Write Gate is true (low).
2 . Th e D i r e c t ion S e lect 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. When the diskette lever is opened.
COM P O SITE WRITE DATA
When the drive is selected, this interface line
p rovides the bit serial Composite Wr it e D a t a
p ulses that control the switching of the Wr i t e
Current in t h e selected head. The wr it e elec-
t ronics must be conditioned for wri t in g by th e
Write Enable line.
For each high-to-low transition on the Compos-
ite Write Data li ne, a flux change 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-
nique is used in which data and clock form the
c ombined W r i t e D a t a s i g n al , i t i s r e c o m -
mended that th e repetition of the hi gh -to-low
transitions, while wri t in g all zeros, be equal to
the nominal data r a te, ~ 0 . 1 percent, and th e
repetition of the high-to-low transitions, while
writing all ones, be equal to twice the nominal
data rate, ~ 0.1 percent.
Host controllers may implement write precom-
pensation ci r cuit s t h a t
T M 8 4 8 -2 E
r ate of three
r e c ognize worst ca se
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. Although a value cannot be specified for
w rite p r e compensation, T a n do n s u g gests a
value of 125 nanoseconds for systems using
MFM double density recording format.
WRITE GATE
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 an d
the read electronics are disabled. This signal
turns on W r i t e Cur r ent i n t h e selected Read/
Write head. Data is wr i t t en u nder the control
of the Composite Write Data and Side Select
input li n es. When the Wr it e Gate line 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 Wr it e Gate or Side
Select lines. With th e N P j u m p er i n s t a l l ed, a
diskette cannot be write protected.
C hanges of s t at e o f t h e W r i t e
G ate l i n e
the first Write Data pulse.
IN USE
This strappable feature controls the lever lock
solenoid when the DL option is installed.
WRITE CURRENT SWITCH
Normally, Wr it e Cu r r ent sw i t c h ing i s accom-
p lished by t h e h o s t c o n t r oller. A t r u e ( l o w )
l evel on t hi s l i n e r e duces the W r i t e C u r r ent .
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 all y
reduces Write Current at Track 43.
SIDE SELECT
The Side Select int er f ace line, available only
on Tandon's TM848-2E, defines which side of
a two-sided di skett e i s
w riting. A n o p e n c i r c u it , f a l s e ( h i gh ) l e v el
3-4
NOTE
s h o ul d o c cur b e f o r e
u s e d f o r r e a d in g o r