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4.1.7
WRITE MODE
A Write operation records data on the diskette in the form of flux reversals. To write data on the
diskette, certain timing relationships must be ensured. These relationships are required to avoid
erasure of data due to hardware failure, unstabilized head position, or head in transit conditions (see
Figure 2-8). The Write circuitry is enabled by activating the Write Gate interface line.
4.1.8
ERASE MODE
The Erase circuitry is also enabled by activating the Write Gate interface line and the erase currents
are applied to the R/W head erase coils when writing data. The erase poles erase an area just to each
side of a track. This ensures off-track reading ability and provides capability to read during worst-
case conditions.
4.1.9
READ MODE
A Read operation retrieves previously recorded data from the selected diskette. This is accom-
plished by the winding in the read head sensing flux reversals on the diskette. The Read mode is
entered on a selected disk drive by deactivating the Write Gate line. Certain timing relationships
are required to ensure stabilization of the R/W head position (see Figure 2-8).
4.1.10
POWE R-DOWN MODE
When the +5V supply drops to an unsafe level during DC power-down, all Write and Erase cir-
cuitry is deactivated to prevent inadvertent writing or erasing on the diskette.
4.1.11
SPINDLE DRIVE MOTOR
The spindle drive motor is a DC motor with an integral tachometer. It is activated by a separate
Motor On interface line. This motor requires approximately one second to attain stabilized speed.
The Motor On signal turns on a current driver that applies current to the motor windings. The
phase of the tachometer output voltage is compared with the phase of a reference oscillator. Any
phase error is converted to a voltage that is added to a constant voltage. The sum is applied to the
motor drive circuit which increases or decreases the motor speed, as required, to keep the tachom-
eter phase-locked with the reference oscillator (see paragraphs 5.8.1 - 5.8.2).
4-4
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