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8.2.1 Port A (Route 0) Switches and Indicators
• Toggle Switch
• RSV (LED)
• SEL (LED)
In the "E" (Enable) position, this switch establishes a
communications channel (route 0) between the disk drive
and a drive controller.
In the "D" (Disable) position, no com,munications chan-
nel is established between the disk drive and the drive
controller.
When lit, indicates that the D2246 is priority-selected by
the route 0 controller.
When lit, indicates that the D2246 is selected by the route
o
controller.
8.2.2 Port B (Route 1) Switches and Indicators
• Toggle Switch
• RSV (LED)
• SEL (LED)
In the "E" (Enable) position, this switch establishes a
communications channel (route 1) between the disk drive
and a drive controller.
In the "D" (Disable) position, no communications chan-
nel is established between the disk drive and the drive
controller.
When lit, indicates that the D2246 is priority-selected by
the route 1 controller.
When lit, indicates that the D2246 is selected by the route
1 controller.
8.2.3 Release Timer: ON/OFF Switch
This switch controls the release timer, a device that allows alternate controller access to
the drive. With this switch in the OFF position, a drive remains selected until specifically
released by the controller (see Section 8.5.l).
With this switch in the ON position, the release timer automatically manages controller
access. Each controller is allowed approximately 500 milliseconds of disk time. After that
period, the communications channel is disabled and drive access is granted to the other
controller.
8.3 DRIVE SELECTION
Drive selection is controlled by the G9QSW PCB on the Dual-Port Interface. When no
controller has the drive reserved, the drive is available and can be selected or reserved by
either controller. The interface recognizes and engages with the first controller to
complete a drive selection. The drive is reserved by the selecting controller, and remains
reserved until a Release signal, a release timer function, or a dc power-down occurs.
If the drive is already reserved or selected, a Busy signal is issued on cable A of the
controller attempting the select. This Busy signal is issued within 600 ns of the selection
attempt and remains until the drive is no longer reserved or selected.
8-3
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