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FUNCTIONAL DESCRIPTION
D6
Head Select - This bit selects which side of the flexible disc is being accessed.
A low signal on this
line selects the upper ( Head 1) side of the flexible disc.
D4
Step-Floppy - When this signal is a low pulse, the flexible disc drive head is stepped one track.
D3
Direction Select - When
this bit is a zero and the drive is stepped, it will step toward the center
track and vica versa.
D2
Disc Change Reset - When this bit is taken low and then back high while a flexible disc is installed,
it clears the flexible disc drive Change Signal.
PHASE-LOCK
~LOOP's AND DRIVE INTERFACE
The 3 1/2-inch Winchester and flexible disc drives are interfaced to the Disc Controller through two buf-
fers and two PLLs. The Drive Signals: Sector, Fault, Index, 4 MHz clock, Write Gate, Write NIC (Controller
IC on the Winchester
drive) control signal, and Write Data interface directly to the Disc Controller chip
through buffers.
Read Data from the flexible disc drive is first received by a Schmitt Trigger Inverter.
The
Schmitt Trigger helps clean up the data line before it is interpreted by the PLL.
The digital PLL recovers
the Read Clock from the flexible disc drive Read Data line.
The Winchester disc data is also cleaned up by a Schmitt Trigger before being passed on to an Analog PLL.
The PLL separates the clock and data from the Raw Read Data.
The Disc Controller controls when the PLL
should provide data by using the Read Gate signal, while the PLL indicates to the Disc Controller when it is
synchronized with the disc data using the In-Sync line.
5-8
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