ICS9147-12 Datasheet, PDF (4/9 Pages) Integrated Circuit Systems – Pentium/ProTM System and Cyrix™ Clock Chip

ICS9147-12
Technical Pin Function Descriptions
VDD(1,2,3,4)
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, 48/24MHz and SDRAM(0:7).
This supply operates at 3.3 volts. Clocks from the listed
buffer 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
This is the power supply for the CPUCLK and IOAPIC output
buffers. The voltage level for these outputs may be 2.5 or 3.3
volts. 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
This is the power supply ground (common or negative) return
pin for the internal core logic and all the 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. See the data tables for the value of this
capacitor. Also includes feedback resistor from X2.
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 that is connected to ground. See the Data
Sheet for the value of this capacitor.
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.
SDRAM(0:7)
These Output Clocks are use to drive Dynamic RAM’s and
are low skew copies of the CPU Clocks. The voltage swing of
the SDRAM’s output is controlled by the supply voltage
that is applied to VDD3 of the device, operating at 3.3 volts.
48MHz
This is a fixed frequency Clock output at 48MHz that is
typically used to drive USB devices.
24MHz
This pin is a fixed frequency clock output typically used to
drive Super I/O devices.
IOAPIC
This Output is a fixed frequency Output Clock that runs at
the Reference Input (typically 14.31818MHz) . Its voltage
level swing is controlled by VDDL and may operate at 2.5 or
3.3volts.
REF(0:2)
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 equivalent to PCICLK(0:5) and is FREE
RUNNING.
PCICLK (0:5)
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 1/2 CPU frequency, or CPU/
2.5; see frequency table.
FS0,1,2
These Input pins control the frequency of the Clocks at the
CPU, PCICLK and SDRAM output pins. See frequency table.
The level of FS2 is latched at power-on, defined by a series
resistor (typically 10K ohm) to VDD or GND.
PD#
This input pin stops all clocks in the low state and powers
down the oscillator and VCOs.
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