ICS9148-18 Datasheet, PDF (3/11 Pages) Integrated Circuit Systems – Pentium/ProTM System Clock Chip

ICS9148-18
Technical Pin Function Descriptions
VDD(1,2)
This is the power supply to the internal core logic of the
device as well as the clock output buffers for REF0, PCICLK
(0:4), and PCICLK_F.
This pin operates at 3.3V volts. Clocks from the 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
This is the power supply for the CPUCLK output buffers.
The voltage level for these outputs may be 2.5 or 3.3volts.
Clocks from the buffers that this pin supplies will have a
voltage swing from Ground to VDDL. For the actual
guaranteed high and low voltage levels of these Clocks,
please consult the DC parameter table in this data sheet.
GND(1,2)
This is the power supply ground (common or negative) return
pin for the internal core logic and all the PCI output buffers.
GNDL
This is the ground for CPUCLK 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 crystal. When the device
is driven by an external clock signal, X1 is the device input
pin for that reference clock. This pin also has 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 crystal. The
X2 pin also has an internal loading capacitor, nominally 33pF.
CPUCLK (0:1)
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 VDDL 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.
REF0
The REF Output is fixed frequency clock that runs at the
same frequency as the Input Reference Clock or the Crystal
(typically 14.31818MHz) attached across X1 and X2.
PCICLK_F
This Output is equal to PCICLK(0:4) and is FREE RUNNING,
and will not be stopped by PCI_STOP#.
PCICLK (0:4)
These output clocks generate all the PCI timing requirements
for a Pentium/Pro based system. They conform to the
current PCI specification.
SELECT 100/66.6MHz#
This input pin controls the frequency of the clocks at the
CPU & PCICLK output pins. If a logic “1” value is present on
this pin, the 100MHz clock is selected. If a logic “0” is used,
the 66.6MHz frequency is selected. The PCI clock is
multiplexed to run at 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).
PD#
This is an asynchronous active low input pin used to power
down the device into a low power state. The internal clocks
are disabled and the VCO and Crystal are stopped. Power
down will also place all the outputs in a low state at the end of
their current cycle. The latency of power down will not be
greater than 3ms.
CPU_STOP#
This is a synchronous active low input pin used to stop the
CPUCLK clocks in an active low state. All other clocks will
continue to run while this function is enabled. The CPUCLKs
will have a turn ON latency of at least 3 CPU clocks.
PCI_STOP#
This is a synchronous active low input pin used to stop the
PCICLK clocks in an active low state. It will not effect
PCICLK_F nor any other outputs.
3