Chapter 6. System Compatibility
3. Sends the EOI
4. Waits one I/O delay
5. Enables the interrupt through the Set Interrupt Enable Flag command
Hardware interrupt IRQ9 is defined as the replacement interrupt level for the cascade level IRQ2.
Program interrupt sharing is implemented on IRQ2, interrupt hex 0A. The following processing occurs to
maintain compatibility with the IRQ2 used by IBM Personal Computer products:
1. A device drives the interrupt request active on IRQ2 of the channel.
2. This interrupt request is mapped in hardware to IRQ9 input on the second interrupt controller.
3. When the interrupt occurs, the system microprocessor passes control to the IRQ9 (interrupt hex 71)
interrupt handler.
4. This interrupt handler performs an EOI command to the second interrupt controller and passes control
to the IRQ2 (interrupt hex 0A) interrupt handler.
5. This IRQ2 interrupt handler, when handling the interrupt, causes the device to reset the interrupt
request before performing an EOI command to the master interrupt controller that finishes servicing
the IRQ2 request.
Diskette Drives and Controller
The following figures show the reading, writing, and formatting capabilities of each type of diskette drive.
Notes:
1. Do not use either a 250/500 KB or 300/500 KB diskette drive for 5.25-inch diskettes that are designed
for the 1.2MB mode.
2. Low-density 5.25-inch diskettes that are written to or formatted by a high-capacity 1.2 MB diskette
drive can be reliably read only by another 1.2 MB diskette drive.
Copy Protection
The following methods of copy protection might not work in systems using the 3.5-inch 1.44 MB diskette
drive.
Bypassing BIOS routines
– Data transfer rate: BIOS selects the proper data transfer rate for the media being used.
– Diskette parameter table: Copy protection, which creates its own diskette parameter table, might
not work in these drives.
Figure 22. 5.25-Inch Diskette Drive Reading, Writing, and Formatting Capabilities
Diskette Drive Type
250/500 KB Mode
300/500 KB Mode
1 MB Mode
Single sided (48 Tracks Per Inch
(TPI))
RWF
—
—
Double sided (48 TPI)
RWF
RWF
—
High capacity (1.2 MB)
RWF
RWF
RWF
Figure 23. 3.5-Inch Diskette Drive Reading, Writing, and Formatting Capabilities
Diskette Drive Type
720 KB Mode
1.44 MB Mode
1.44 MB drive
RWF
RWF
2.88 MB drive
RWF
RWF
Chapter 6. System Compatibility
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Содержание PC 300GL Type 6267
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