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Intel
®
440GX AGPset Design Guide
3-5
Design Checklist
3.3.2 Intel
®
Pentium
®
II Processor Clocks
•
Include a circuit for the system bus clock to core frequency ratio to the processor. The ratio
should be configurable as opposed to hard wired. The bus frequency select straps will be
latched on the rising edge of CRESET#.
•
CRESET# is used as the selection signal for muxing A20M#, IGNNE#, INTR, and NMI with
the processor bus/core frequency selection jumpers. A ‘244 buffer maybe used as a mux. The
outputs of the ‘244 device are fed to open collector buffers for voltage translation to the CPU.
See the reference board schematics for specific implementation.
•
PICCLK must be driven by a clock even if an I/O APIC is not being used. This clock can be as
high as 33.3 MHz in a UP system. A DP system utilizing Intel’s I/O APIC (82093AA) has a
maximum PICCLK frequency of 16.666 MHz.
3.3.3 Intel
®
Pentium
®
II Processor
Signals
•
Dual termination (56 ohm) to Vtt of the GTL+ bus is required if the trace length restrictions of
a SET (single-ended termination) environment cannot be met.
•
THERMTRIP# must be pulled-up to Vcc
2.5
(150 ohm to 10K ohm) if used by system logic.
The signal may be wire-OR’ed and does not require an external gate. It may be left as NC if it
is not used. See the Debug Recommendations for further information that may affect the
resistor values.
•
The FERR# output must be pulled up to Vcc2.5 (150 ohm to 10K ohm) and connected to the
PIIX4E. The reference schematics uses 220 ohms. See the Debug Recommendations for
further information that may affect these resistor values.
•
PICD[1:0]# must have 150 ohm pull-ups to Vcc2.5 even if an I/O APIC is not being used. See
the Debug Recommendations for further information that may affect these resistor values.
•
All CMOS inputs should be pulled up to Vcc2.5 (150 ohm to 10K ohm). See the Debug
Recommendations for further information that may affect these resistor values.
•
Be sure the Slot 1 inputs are not being driven by 3.3V or 5V logic. Logic translation of 3.3V or
5V signals may be accomplished by using open-drain drivers pulled-up to Vcc2.5.
•
The PWRGOOD input should be driven to the appropriate level from the active-high “AND”
of the Power-Good signals from the 5V, 3.3V and Vcc
CORE
supplies. The output of any logic
used to drive PWRGOOD should be a Vcc
2.5
level to the processor.
•
No V
REF
should be generated for the Intel
®
Pentium
®
II processor. V
REF
is locally generated
on the processor card.
•
Vtt must have adequate bulk decoupling based on the reaction time of the regulator used to
generate Vtt. It must provide for a current ramp of up to 8A/uS while maintaining the voltage
tolerance defined in the
Intel
®
Pentium
®
II Processor
datasheet.
•
If an on-board voltage regulator is used instead of a VRM, Vcc
CORE
must have adequate bulk
decoupling based on the reaction time of the regulator used to generate Vcc
CORE
. It must
provide for a current ramp of up to 30A/uS while maintaining the VRM 8.2 DC-DC Converter
Specification.
•
The VID lines should have pull-up resistors ONLY if they are required by the Voltage
Regulator Module or on board regulator that you have chosen. The pull-up voltage used should
be to the regulator input voltage (5V or 12V). However, if 12V is used, a resistor divider
should be utilized to lower the VID signal to CMOS/TTL levels. The VID signals may be used
to detect the presence of a processor core. A pull-up is not required unless the VID signals are