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tzt;
p~
~
WR\TE
_;
I
I
150
PROTECT
,;v-
I
I
L.E.D.
~
WRITE:
"'~)
:
2.
+5V
PROTECT
:
I
SENSOR
>;;-:-,- -........- - . - - - -
L_J
RPZ 7
22~
8
TP7
+5V
5 RP4
4.71(,
Figure 3-10
Write Protect Schematic Diagram
Test Points 2 and 3 (see Figure 3-11) are provided to observe the differential output of the first stage
of Read signal preamplification. Test Points 4 and 5 are provided to observe the differential output of
the second stage amplifier and differentiated Read signal. Test Point 9 is the output of thesingle shot
used in the Read section, nominally 200 nanoseconds for each flux transition detected. Test Point 1
is signal ground.
Circuit Description
The read signal comes from the selected head on the drive. It is gated to the preamplifier U7 by the
-Write signal to U25, which forward biases diodes CR14 and CR15. Then, the Read signal passes
through a linear bandpass filter. The Read signal is then input to U2, the differentiator.
The output of U2 goes through the D. C. blocking capacitors to the crossover detector, U8, which
digitizes the signal. This converts the signal into standard TIL level Integrated circuits U9, U11, and
U10 comprise a comparator circuit. Any pulses that occur outside of the normal duty cycle of U 11 are
eliminated. U9 is an edge detector. U11 acts as a one shot, with a timeout of approximately 860
nanoseconds. U1 0 is the actual comparator.
The Read signal is presented to U9. Then it goes to U11, where the pulses are shaped to 200
nanoseconds. This output is gated at U29 with the Unit Select signal to produce a digital output at Pin
46 of the interface connector (see Figure 3-12).
Note
U11, the final one shot, is disabled when the
drive is writing data onto the diskette.
G. Two Sided
Functional Description
This output enables the controller to determine if a diskette is installed, which utilizes the Index 2
index hole. This may be used to indicate to the host controller that a two-sided diskette is in the drive.
3-13
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