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WRITE
PROTECT
L.E.D.
WRITE+
PROTECT
SENMR
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 TTL level Integrated circuits U9, U11, and
corn parator c
U10 comprise a
eliminated. U9 is an edge detector. U11 acts as a one shot, with a timeout of approximately 860
nanoseconds. U10 is the actual comparator.
T he Read signal is presented to U9. Then it g oes to U 1 1, where the p u lses are shaped to 2 0 0
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).
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.
P 3
+~"
IgO
'2
05V
I
RP2
22lC.
Figure 3-10
Write Protect Schematic Diagram
ircuit. Any pulses that occur outside of the normal duty cycle of U11 are
Note
U11, the final one shot, is disabled when the
drive is writing data onto the diskette.
3-1 3
TP7
DRIVEL+ 5
U29
2
I U
36
+ V
5 RP4
4.7K,
M'539
V3?
s
ZZK
4 7 O Kr
RP2
RP3
WRITE
PROTECT
WRPROT-
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