Disk Drive; Read/Write Head; Control And Data Line Character1S.tics; Logic Levels - Control Data Corporation BR8 SERIES Hardware Maintenance Manual

o
cell time.
If
no "one" data bit is present in the composite data, the -Read Data
Separated signal will remain high. At the end of the 3/4 cell timeout, the flip
flop is reset to repeat the operation.
4.3.4 DISK DRIVE
Disk drive is accomplished by clamping the diskette between the cone assembly and a
belt driven spindle. The spindle is rotated at 360 rpm by the disk drive motor. A dual
pulley option permits 50 or 60 Hz operation without a motor change.
4.3.5 READ/WRITE HEAD
The Read/Write head is in direct contact with the diskette during read or write
operation. Since the head is rigidly mounted on the carriage assembly, head load
is achieved by a solenoid actuated bail allowing the head load arm to force the
diskette against the Read/Write head. The head surface is designed for maximum
signal transfer to and from the magnetic surface of the diskette with minimum head/
disk wear. The tunnel erase gap DC-erases the intertrack area to improve off-track
signal-to-noise ratio and permit diskette interchange between units.
4.4 CONTROL AND DATA LINE CHARACTERISTrCS
All signal lines must be terminated at the receiver with a characteristic impedance
of 120 ohms, typically. Transmission is by 26 AWG (min.), 120 ohm flat cable or
twisted pair (one twist per inch) with a maximum line length of 25 feet. Figure 5-1
shows the timing of typical operations.
4.4. 1 LOGIC LEVELS
The following definitions will be used throughout this manual:
low
=
Logic 1, Active State
high
=
Logic 0, Inacti ve state
Refers to the low-voltage condition
+
0.4
VDC Max.
Refers to the high-voltage condition
t
2.4
VDC
Min.
4.4.2 TRANSMITTER CHARACTERISTICS
The FDD uses the TTL7438 (quad 2-input buffer or driver) to transmit all control
and data signals. This transmitter is capable of sinking a current of 48ma with an
output voltage of
O.
4 volt.
4.4.3 LINE RECEIVER CHARACTERISTICS
The FDD uses the SN7400 family gates for line receivers. The input of each receiver
is terminated in 120 ohms.
77834769-A
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