Specifications

158004.B00 45
PC
IRQ
INTERNAL/
EXTERNAL
PnP AWARE? PC/104
BUS?
ALLOCATION
0 Internal Yes No Timer
1 On-Board Yes No Keyboard in PC97317 Super I/O
chip
2 Internal N/A No Cascades second 8259 chip
3 On-Board Yes Yes COM2 in PC97317 Super I/O chip
4 On-Board Yes Yes COM1 in PC97317 Super I/O chip
5 On-Board Yes
(SoundBlaster)
Yes COM3 in extra UART chip, or
SoundBlaster
(See text above).
6 On-Board Yes Yes Floppy Disk drive in PC97317
7 On-Board Yes Yes Printer port in PC97317 Super I/O
chip
8 On-Board Yes No Alarm interrupt from RTC in
PC97317
9 On-Board No Yes COM4 in extra UART chip.
10 Internal
(normally)
No Yes Normally allocated to Ethernet chip.
IRQ10 is present on PC/104 bus.
11 Internal
(USB) or
External (no
USB)
No, except
PnP is aware
of USB
Yes USB default (See text above)
12 On-Board Yes Yes Mouse in PC97317 Super I/O chip
13 Internal Yes No Floating-Point Processor in Geode
GX1
14 On-Board Yes Yes IDE Disk Drive
15 External No Yes
TABLE 9 - INTERRUPT ALLOCATION
Note that the serial ports and printer have individual interrupt enable bits, within their
register sets. The default is for these interrupts to be disabled. This means that IRQ3,
IRQ4, IRQ5, IRQ7 and IRQ9 can be used by other PC/104 or PC/104-Plus boards if
the interrupts are not being used by the serial and printer ports. IRQ12 is available if
the mouse controller is disabled. IRQ14 is available if no IDE drives are fitted.
All the PC/104 bus interrupts are programmed to generate an interrupt on a positive-
going edge.
The Geode GX1 does not have a dedicated NMI pin, so non-maskable interrupts are
not available on the TP400’s PC/104 bus. The SERR# and PERR# pins however may
generate non-maskable interrupts, which are emulated by SMI code.
4.5.2 PC/104-Plus Bus Interrupts
The PC/104-Plus bus (PCI bus) has four interrupt pins, INTA#, INTB#, INTC# and
INTD#. These can be programmed by the BIOS Setup program to cause interrupts
on any of the fifteen IRQ levels.