ICS9148-32 Datasheet, PDF (3/14 Pages) Integrated Circuit Systems – Pentium/ProTM System Clock Chip

ICS9148-32
Technical Pin Function Descriptions
VDD, VDD (1,2,3)
This is the power supply to the internal core logic of the
device as well as the clock output buffers for REF(0:2),
PCICLK_F, PCICLK (0:6), 48MHz0, 48MHz1.
This pin operates at 3.3V volts. Clocks from the listed buffers
that it supplies will have a voltage swing from Ground to this
level. For the actual guaranteed high and low voltage levels
for the Clocks, please consult the DC parameter table in this
data sheet.
VDDL (1,2)
This is the power supply for the CPUCLK (0:3) and IOAPIC
output buffers. The voltage level for these outputs may be
2.5 or 3.3volts. Clocks from the buffers that each supplies will
have a voltage swing from Ground to this level. For the actual
Guaranteed high and low voltage levels of these Clocks,
please consult the DC parameter table in this Data Sheet.
GND, GND (1,2,3)
This is the ground to the internal core logic of the device as
well as the clock output buffers for REF(0:2), PCICLK_F,
PCICLK (0:6), 48MHz 0, 48MHz1.
GNDL (1,2)
This is the ground for the CPUCLK (0:3) and IOAPIC output
buffers.
X1
This input pin serves one of two functions. When the device
is used with a Crystal, X1 acts as the input pin for the
reference signal that comes from the discrete crystal. When
the device is driven by an external clock signal, X1 is the
device input pin for that reference clock. This pin also
implements an internal Crystal loading capacitor that is
connected to ground. With a nominal value of 33pF no
external load cap is needed for a C_L=17 to 18pF crystal.
X2
This Output pin is used only when the device uses a Crystal
as the reference frequency source. In this mode of operation,
X2 is an output signal that drives (or excites) the discrete
Crystal. The X2 pin will also implement an internal Crystal
loading capacitor nominally 33pF.
CPUCLK (0:3)
These Output pins are the Clock Outputs that drive processor
and other CPU related circuitry that requires clocks which are
in tight skew tolerance with the CPU clock. The voltage
swing of these Clocks is controlled by the Voltage level
applied to the VDDL2 pin of the device. See the Functionality
Table for a list of the specific frequencies that are available
for these Clocks and the selection codes to produce them.
48MHz
This is a fixed frequency Clock output that is typically used
to drive USB devices.
24/48MHz
Fixed frequency clock output. 24MHz output if Pin1=1 at
power up. 48MHz if pin1=0 at power up.
IOAPIC (0:1)
This Output is a fixed frequency Output Clock that runs at
the Reference Input (typically 14.31818MHz) . Its voltage
level swing is controlled by VDDL1 and may operate at 2.5 or
3.3volts.
REF0/SEL 48#
This is an input pin during power up only. During power up if
high, then pin 23 is a 24MHz fixed clock during normal
operation. If Low during power up, pin 23 is a 48MHz fixed
clock during normal operation. During normal operation, REF0
is an output which is a fixed frequency running at 14.318MHz.
REF(1:2)
The REF Outputs are fixed frequency Clocks that run at the
same frequency as the Input Reference Clock X1 or the
Crystal (typically 14.31818MHz) attached across X1 and X2.
PCICLK_F
This Output is equal to PCICLK(0:6) and is FREE RUNNING,
and will not be stopped by PCI_STOP#.
PCICLK (0:6)
These Output Clocks generate all the PCI timing requirements
for a Pentium/Pro based system. They conform to the current
PCI specification. They run at 33.3 MHz.
SEL 100/66.6#
This Input pin controls the frequency of the Clocks at the
CPUCLK, PCICLK and SDRAM output pins. If a logic “1”
value is present on this pin, the 100MHz Clock will be selected.
If a logic “0” is used, the 66.6MHz frequency will be selected.
The PCI clock is multiplexed to be 33.3MHz for both select
cases. PCI is synchronous at the rising edge of PCI to the
CPU rising edge (with the skew making CPU early).
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