40, 39, 36,
8, 10, 11, 13,
14, 16, 17
1, 2, 47
25, 26, 27
9, 15, 19, 21,
3, 6, 12, 18,
20, 24, 32,
34, 38, 43
CPU Clock Outputs 0 through 3: These four CPU clock outputs are controlled by
the CPU_STOP# control pin. Output voltage swing is controlled by voltage applied
PCI Bus Clock Outputs 1 through 7: These seven PCI clock outputs are con-
trolled by the PCI_STOP# control pin. Output voltage swing is controlled by voltage
applied to VDDQ3.
Fixed PCI Clock Output: Unlike PCI1:7 outputs, this output is not controlled by the
PCI_STOP# control pin. Output voltage swing is controlled by voltage applied to
CPU_STOP# Input: When brought LOW, clock outputs CPU0:3 are stopped LOW
after completing a full clock cycle (2–3 CPU clock latency). When brought HIGH,
clock outputs CPU0:3 start beginning with a full clock cycle (2–3 CPU clock latency).
PCI_STOP# Input: The PCI_STOP# input enables the PCI 1:7 outputs when HIGH
and causes them to remain at logic 0 when LOW. The PCI_STOP signal is latched
on the rising edge of PCI_F. Its effects take place on the next PCI_F clock cycle.
SPREAD# Input: When brought LOW this pin activates Spread Spectrum clocking.
I/O APIC Clock Outputs: Provides 14.318-MHz fixed frequency. The output volt-
age swing is controlled by VDDQ2.
48-MHz Outputs: Fixed clock outputs at 48 MHz. Output voltage swing is controlled
by voltage applied to VDDQ3.
Fixed 14.318-MHz Outputs 0 through 2: Used for various system applications.
Output voltage swing is controlled by voltage applied to VDDQ3.
Frequency Selection Input: Selects power-up default CPU clock frequency as
shown in Table 1 on page 1.
Crystal Connection or External Reference Frequency Input: Connect to either
a 14.318-MHz crystal or reference signal.
Crystal Connection: An input connection for an external 14.318-MHz crystal. If
using an external reference, this pin must be left unconnected.
Power Down Control: When this input is LOW, device goes into a low-power
condition. All outputs are held LOW while in power-down. CPU and PCI clock out-
puts are stopped LOW after completing a full clock cycle (2–3 CPU clock cycle
latency). When brought HIGH, CPU, SDRAM and PCI outputs start with a full clock
cycle at full operating frequency (3 ms maximum latency).
Power Connection: Connect to 3.3V supply.
Power Connection: Power supply for CPU0:3 and APIC0:1 output buffers. Con-
nect to 2.5V supply or 3.3V supply.
Ground Connection: Connect all ground pins to the common system ground
No Connect: Do not connect.
Document #: 38-07192 Rev. *A
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