Hardware Reference
In-Depth Information
Noticethatinterrupts0,1,2,8,and13arenotonthebusconnectorsandarenotaccessible
to adapter cards. Interrupts 8,10,11,12,13,14,and 15are from the second interrupt con-
troller and are accessible only by boards that use the 16-bit extension connector because
this is where these wires are located. IRQ9 is rewired to the 8-bit slot connector in place
of IRQ2, so IRQ9 replaces IRQ2 and, therefore, is available to 8-bit cards, which treat it
as though it were IRQ2.
Note
Although the 16-bit ISA bus has twice as many interrupts as systems that have the 8-bit ISA
bus, you still might run out of available interrupts because only 16-bit adapters can use most
of the newly available interrupts. Any 32-bit PCI adapter can be mapped to any ISA IRQs.
The extra IRQ lines in a 16-bit ISA system are of little help unless the adapter boards
you plan to use enable you to configure them for one of the unused IRQs. Some devices
are hard-wired so they can use only a particular IRQ, and some of the early 16-bit ISA
adapters weren't designed to use 16-bit IRQs (9-15). If you have a device that already
usesthatIRQ,youmustresolvetheconflictbeforeinstallingthesecondadapter.Ifneither
adapter enables you to reconfigure its IRQ use, chances are that you can't use the two
devices in the same system.
