Intel 820E manual Interrupt Interface, Pirq#Da, Pirq#H, Pirq#E, Apic

					Intel® 820E Chipset
	R
Table 31. Interrupt Interface
		Checklist Items		Recommendations	Reason/Effect
		PIRQ#[D:A]	These signals require a pull-up		In a non-APIC mode, the PIRQx# signals can be
			resistor. A 2.7 kΩ pull-up resistor		routed to interrupts 3, 4, 5, 6, 7, 9, 10, 11, 12, 14 or
			to VCC 5 V or an 8.2 kΩ pull-up		15. Each PIRQx# line has a separate Route Control
			resistor to VCC 3.3 V is		Register.
			recommended.		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] /	These signals require a pull-up		In non-APIC mode, the PIRQx# signals can be
		GPIO[4:3]	resistor. Recommend a 2.7 kΩ		routed to interrupts 3, 4, 5, 6, 7, 9, 10, 11, 12, 14 or
			pull-up resistor to VCC 5 or an		15. Each PIRQx# line has a separate Route Control
			8.2 kΩ pull-up resistor to VCC		Register.
			3.3.		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]	These signals require a pull-up		In a non-APIC mode, the PIRQx# signals can be
		PIRQ#[E]	resistor. A 2.7 kΩ pull-up resistor		routed to interrupts 3, 4, 5, 6, 7, 9, 10, 11, 12, 14 or
			to VCC 5 or an 8.2 kΩ pull-up		15. Each PIRQx# line has a separate Route Control
			resistor to VCC 3.3 is		Register.
			recommended.		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		If the APIC is not used on UP systems:
				150 Ω pull-up resistors on	Use pull-downs for each APIC signal. Do not share
				APICD[0:1] ! Same as	a resistor to pull-up signals.
				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 kΩ pull-down
				resistors.

Design Guide 127