3. Theory of Operation
16
INTERRUPTS
The ZT 8954 can drive any of the bussed backplane interrupts, as well as the slot-
specific interrupt IRQx. By default, the ZT 8954 is jumpered for driving INTRQ2*
(backplane pin P50) for the floppy disk subsystem interrupt.
The "Interrupt Selections" illustration below indicates the possible interrupt selections.
† W16 is installed by default.
Floppy
Disk
Controller
IRQx
INTRQ*
INTRQ1*
INTRQ2*
INTRQ3*
INTRQ4*
(E47)
(P44)
(P37)
(P50)
(E67)
(P5)
126
W12
W13
W14
W15
W16
W17
W18
†
Interrupt Selections
ZIATECH STD 32 STAR SYSTEM USE
In multiprocessing operations, the floppy disk interface is shared between CPUs in the
backplane. Because different CPU boards are supported by different floppy disk
interfaces, the STD 32 STAR SYSTEM allows for different CPU board types. When a
system is composed of different CPU types, a simple rule is applied, as detailed in the
following topic, "STAR SYSTEM Floppy Rule".
STAR SYSTEM Floppy Rule
Always match the floppy disk controller to the Permanent Master type. For instance, if
the ZT 8902 Rev A is your Permanent Master, the ZT 8954 is required. The STAR BIOS
will manage transfers between Temporary Masters and the floppy disk through the
Permanent Master.
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