Sharp MZ-80SFD Service Manual page 5

6) Write protect detection section
A luminous diode and a photo-transistor are used
to detect write protect notch of the diskette and
jacket. (Writing is not possible when the notch is
covered with labeL)
Center hole
Head
window
Label area
Index hole
Write
protect
notch
3. Interface
1)
Interface signal
All lines are of TTL (transistor-transistor logic).
(1)
Input signals
For input signals there are 10 kinds of input lines,
all of which are valid at low levels. These signal
lines are terminated at a 150-ohm
int~rated
resistor fitted in the IC socket of drive 1. The
signal voltage levels are as follows.
High level
I
Invalid 2.4 to 5.25V
Low level
I
Valid
o
to OAV
Input impedance Pull-up to 5V at 150-ohm
resistor
Description of diskette parts
7)
Index detection section
This section consists of a luminous diode and a
phototransistor. An index hole of the diskette is
detected by this section to determ ine the starting
point of a track.
8) Track 00 detection section
A carriage position is detected with a limit switch.
When the carriage has reached the track 00 point,
track 00 signal is emitted.
9)
Control electronics section
The electric circuit to control each mechanism is
composed of 2 sheets of PWB. One is to control
the DC motor control circuit. The other is to
control other circuits, say, detection and other
functions with respect to read/write, step, head
load, and other signals.
10) Diskette protect mechanism
Shutting the front door, with the diskette incom-
pletely set in, can give damage to the diskette, thus
shortening its life-time. To prevent such a draw-
back, this mechanism has been adopted so that the
front door connot
be
closed if the diskette is
improperly in.
-3-
CD
Drive select signals (0 to
3)
MZ-80SFD is connectable up to 4 units.
These signals are used to select a desired one of
the four drive units.
At low levels of drive select signal,
RIW
head is
loaded to cause the operation indicator to light up.
Note)
The drive requires to
be
set with a drive select
switch to meet the position of use (Drive No. 1
thru 4).
@
Motor ON signal
The drive motor starts when the signal level
be-
comes low. This signal level becomes high about
2 seconds after completion of all operations, if
no operation is commanded next. It thus inter-
rupts the motor, extending the service life of
motor.
@
Direction select signal
The signal is given to designate the shifting
direction of R IW head, when the step pulse is
input.
High level- - . Out direction (to diskette outer
portion)
Low level - - - IN direction (to diskette center)
@Step signal
This signal is given to move the RNoJ head in the
direction designated by the direction select signal.
The operation is done in the course of changing
from low levels to high levels.