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Intel
®
820E Chipset
R
Design Guide 127
Table 31. Interrupt Interface
Checklist Items Recommendations Reason/Effect
PIRQ#[D:A] These signals require a pull-up
resistor. A 2.7 k
Ω pull-up resistor
to V
CC
5 V or an 8.2 kΩ pull-up
resistor to V
CC
3.3 V is
recommended.
In a non-APIC mode, the PIRQx# signals can be
routed to interrupts 3, 4, 5, 6, 7, 9, 10, 11, 12, 14 or
15. Each PIRQx# line has a separate Route Control
Register.
In the APIC mode, these signals are connected to
the internal I/O APIC, as follows: PIRQ[A]# is
connected to IRQ16, PIRQ[B]# to IRQ17, PIRQ[C]#
to IRQ18, and PIRQ[D]# to IRQ19. This frees the
ISA interrupts.
PIRQ#[G:F] /
GPIO[4:3]
These signals require a pull-up
resistor. Recommend a 2.7 k
Ω
pull-up resistor to V
CC
5 or an
8.2 k
Ω pull-up resistor to V
CC
3.3.
In non-APIC mode, the PIRQx# signals can be
routed to interrupts 3, 4, 5, 6, 7, 9, 10, 11, 12, 14 or
15. Each PIRQx# line has a separate Route Control
Register.
In APIC mode, these signals are connected to the
internal I/O APIC, as follows: PIRQ[E]# is
connected to IRQ20, PIRQ[F]# to IRQ21, PIRQ[G]#
to IRQ22, and PIRQ[H]# to IRQ23. This frees the
ISA interrupts.
PIRQ#[H]
PIRQ#[E]
These signals require a pull-up
resistor. A 2.7 k
Ω pull-up resistor
to V
CC
5 or an 8.2 kΩ pull-up
resistor to V
CC
3.3 is
recommended.
In a non-APIC mode, the PIRQx# signals can be
routed to interrupts 3, 4, 5, 6, 7, 9, 10, 11, 12, 14 or
15. Each PIRQx# line has a separate Route Control
Register.
In the APIC mode, these signals are connected to
the internal I/O APIC, as follows: PIRQ[E]# is
connected to IRQ20, PIRQ[F]# to IRQ21, PIRQ[G]#
to IRQ22, and PIRQ[H]# to IRQ23. This frees the
ISA interrupts. If not needed for interrupts, these
signals can be used as GPIO.
APIC
•
If the APIC is used
150 Ω pull-up resistors on
APICD[0:1] ! Same as
SC242 checklist: PICD[0:1]
Connect APICCLK to
CK133, with a 20
Ω to 33 Ω
series termination resistor.
• If the APIC is not used on UP
systems
APICCLK can either be tied
to GND or connected to
CK133, but cannot be left
floating.
Pull APICD[0:1] to GND
through 10 k
Ω pull-down
resistors.
If the APIC is not used on UP systems:
Use pull-downs for each APIC signal. Do not share
a resistor to pull-up signals.