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Chapter 3
Interrupt Channel Assignments
The channel interrupt assignments are shown in Table 3-1.
Table 3-1. Interrupt Channel Assignments
Device vs IRQ No.
Timer
Keyboard
Secondary
Cascade
COM1
COM2
COM3
COM4
Floppy
Parallel
RTC
IDE Primary
IDE Secondary
Math Coprocessor
PS/2 Mouse
PCI INTA
PCI INTB
PCI INTC
PCI INTD
PCI INTE
PCI INTF
PCI INTH
Legend: D = Default, O = Optional, X = Fixed
NOTE
The IRQs for the Ethernet, Video, and Internal Local Bus (ISA) are
automatically assigned by the BIOS Plug and Play logic. Local IRQs
assigned during initialization can not be used by external devices.
Memory Map
The following table provides the common PC/AT memory allocations. Memory below 000500h is used
by the BIOS.
LittleBoard 800
0
1
2
3
4
5
X
X
X
O
O
D
O
O
D
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
D
O
O
O
O
O
O
O
D
O
O
O
O
O
O
O
D
O
O
O
O
O
O
O
D
Reference Manual
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7
8
9
10 11
O
O
O
O
O
O
O
O
O
O
O
O
O
O
D
O
O
O
D
O
X
O
D
O
O
O
X
O
O
O
O
O
O
O
O
O
D
O
O
O
O
O
O
O
D
O
O
O
O
O
O
O
O
O
D
O
O
O
O
O
O
O
Hardware
12
13
14
15
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
X
X
X
X
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
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