Mitsubishi Apricot MS Series, Owner'S Handbook Manual

Page: 44 / 87

OWNER’S HANDBOOK
E x p a n s i o n C a r d s 4 / 3
ISA Interrupt request level (IRQ)
The “interrupt request level” or “IRQ” is the means
by which the expansion card sends a signal to get the
attention of, or interrupt, the processor. Your PC has
interrupt levels numbered IRQ0 to IRQ15, many of
which are needed for components on the computer’s
motherboard. There are two ways round this.
♦
Many motherboard components are Plug and
Play (PnP) devices. If you use BIOS Setup or
Windows Control Panel to exclude or reserve an
interrupt that is usually assigned to one of these
devices, an alternative interrupt will be assigned
through Plug and Play and the original interrupt
can instead be used by the expansion card.
♦
You can disable some motherboard components
either by means of the BIOS Setup utility or else
by changing jumper settings on the
motherboard. This frees the resources used by
those components.
See the BIOS Setup & POST chapter for more
information about BIOS Setup. See the Motherboard
Features & Upgrades chapter for more information
about jumper settings and the usual assignment of
interrupts to motherboard components.
Direct memory access (DMA) channel
Some hardware devices can use a “DMA channel” to
access system memory without directly burdening the
processor. Your PC has DMA channels numbered
DMA0 to DMA7. As with interrupts, you can use
vacant channels or re-assign existing ones.
See the Motherboard Features & Upgrades chapter for
more information about the usual assignment of
DMA channels.
Base input/output (I/O) port address
I/O ports are used by the processor to communicate
with hardware devices. Each port appears to the
processor as an address low down in its address space.
Some expansion cards are also controlled by I/O
ports. The “base I/O port address” specifies where the
card’s ports begin.