Read Circuit Operation; Drive Motor Control - Zenith Z-100 PC series Service Manual

4.5
READ CIRCUIT OPERATION
a, Duration of all read operations is under control of the using system.
b. As long as the drive is selected and WRITE GATE is not active, the read signal is amplified and
shaped and the square wave signals are sent to the interface as READ DATA
When the using system requires data from the diskette drive, the using system must select the head and disable
WRITE GATE, The read signal is then fed to the amplifier section of the read circuit. After amplification. the read
signal is fed to a filter where the out of band noise is removed. The read signal is then fed to the differentiator
amplifier.
Since a clock pulse occurs at least once every 8
/LS
and data bits are present once every 4 p.s. the frequency of the
READ DATA varies (FM encoding only). The read signal amplitude decreases as the frequency increases. Note
the signals in figure 4-8. The differential amplifier will amplify. differentiate. limit. and digitize the read signals (sine
waves) ,
The drive has no data separator. only a pulse standardizer for the READ DATA signal.
ERASE 1 ____________
~
ERASEO----------~
+
12V
-j
~
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SIDE 1
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READ DATA
L ___
SELECT 1
SELECT 0
+5 V REG
LSI
' - - , - - - - j
READ
+
READ ENABLE
L....-~
_ _
--I
CH IP
-
FIGURE
4·8. READ CIRCUIT
4.6
DRIVE MOTOR CONTROL
a. Start / Stop
b. Speed Control
c. Over Current Protection
d. Speed Adjustment
The motor used in the SA455/465 is a dc drive motor with a separate motor on and off interface line. After ac­
tivating the MOTOR ON line. a 500 ms delay must be introduced to allow proper motor speed before reading or
writing.
When MOTOR ON is activated at pin 16 of the interface. the mode will start by means of current flow through the
motor windings. The motor speed control utilizes an integral brushless tachometer. The output voltage signal from
this tachometer is compared to a voltage/frequency reference level. The output from the voltage/frequency com­
parator will control the necessary current to maintain a constant motor speed of 300 rpm. Motor speed adjustment
changes the voltage reference through a potentiometer.
4·5
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SIDE 0
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