Table of Contents
Advertisement
NOTE
TM848-1E
and TM848-2E
drives include a microprocessor-
controlled buffered seek capa-
bility. The controller may issue
step pulses of one microsecond
minimurn width, and fifteen
microseconds minimurn spacing
between trailing edges. Internal
drive electronics issue step com-
mands at a rate of three
milliseconds.
The drive electronics ignore step pulses when
one of five conditions exists:
1.
The Write Gate is true (low).
2. The Direction Select is false (high),
and the head is positioned at Track
o.
3. The drive is not selected.
4. When trying to seek beyond Track 76.
5. When the diskette lever is opened.
COMPOSITE WRITE DATA
When the drive is selected, this interface line
provides the bit serial Composite Write Data
pulses that control the switching of the Write
Current in the selected head. The write elec-
tronics must be conditioned for writing by the
Write Enable line.
For each high-to-low transition on the Compos-
ite Write Data line, a flux change is produced
at the write head gap. This causes a flux
change to be recorded on the media.
When a double-frequency type encoding tech-
nique is used in which data and clock form the
combined Write Data signal, it is recom-
mended that the repetition of the high-to-Iow
transitions, while writing all zeros, be equal to
the nominal data rate, ±0.1 percent, and the
repetition of the high-to-Iow transitions, while
writing all ones, be equal to twice the nominal
data rate, ± 0.1 percent.
Host controllers may implement write precom-
pensation circuits that recognize worst case
3-4
patterns and adjust the Write Data wave-
form. Although a value cannot be specified for
write precompensation, Tandon suggests a
value of 125 nanoseconds for systems using
MFM double density recording format.
WRITE GATE
When this signal is true (low), the write
electronics are prepared for writing data and
the read electronics are disabled. This signal
turns on Write Current in the selected Read/
Write head. Data is written under the control
of the Composite Write Data and Side Select
input lines. When the Write 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 Write Gate or Side
Select lines. With the NP jumper installed, a
diskette cannot be write protected.
NOTE
Changes of state of the Write
Gate line should occur before
the first Write Data pulse.
INUSE
This strappable feature controls the lever lock
solenoid when the DL option is installed.
WRITE CURRENT SWITCH
Normally, Write Current switching is accom-
plished by the host controller. A true (low)
level on this line reduces the Write Current.
Using option IC, the drive automatically
reduces Write Current at Track 43.
SIDE SELECT
The Side Select interface line, available only
on Tandon's TM848-2E, defines which side of
a two-sided diskette is used for reading or
writing. An open circuit, false (high) level
Advertisement
Table of Contents
