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 pull-up resistor
to VCC 5 V or an 8.2 k pull-up
resistor to VCC 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
pull-up resistor to VCC 5 or an
8.2 k pull-up resistor to VCC
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 pull-up resistor
to VCC 5 or an 8.2 k pull-up
resistor to VCC 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 pull-up resistors on
APICD[0:1] ! Same as
SC242 checklist: PICD[0:1]
Connect APICCLK to
CK133, with a 20 to 33
series termination resistor.
If t he 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 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.