ICST AV9248F-20, ICS9248F-20 Datasheet
Integrated
Circuit
Systems, Inc.
General Description Features
ICS9248-20
Block Diagram
Pentium/ProTM System Clock Chip
9248-20 Rev B 12/03/98
Pin Configuration
48-Pin SSOP
Pentium is a trademark on Intel Corporation.
Generates system clocks for CPU, IOAPIC, PCI, plus
14.314 MHz REF (0:2), USB, and Super I/O
Supports single or dual processor systems
Supports Spread Spectrum modulation for CPU & PCI
clocks, down spread -0.5%
Skew from CPU (earlier) to PCI clock (rising edges for
100/33.3MHz) 1.5 to 4ns
Two fixed outputs at 48MHz.
Separate 2.5V and 3.3V supply pins
2.5V or 3.3V output: CPU, IOAPIC
3.3V outputs: PCI, REF, 48MHz
No power supply sequence requirements
Uses external 14.318MHz crystal, no external load cap
required for C
L
=18pF crystal
48 pin 300 mil SSOP
The ICS9248-20 is a Clock Synthesizer chip for Pentium and
PentiumPro CPU based Desktop/Notebook systems that will
provide all necessary clock timing.
Features include four CPU and eight PCI clocks. Three
reference outputs are available equal to the crystal frequency.
Additionally, the device meets the Pentium power-up
stabilization requirement, assuring that CPU and PCI clocks
are stable within 2ms after power-up.
PD# pin enables low power mode by stopping crystal OSC
and PLL stages. Other power management features include
CPU_STOP#, which stops CPU (0:3) clocks, and PCI_STOP#,
which stops PCICLK (0:6) clocks.
High drive CPUCLK outputs typically provide greater than 1
V/ns slew rate into 20pF loads. PCICLK outputs typically
provide better than 1V/ns slew rate into 30pF loads while
maintaining 50±5% duty cycle. The REF clock outputs typically
provide better than 0.5V/ns slew rates.
The ICS9248-20 accepts a 14.318MHz reference crystal or
clock as its input and runs on a 3.3V core supply.
Power Groups
VDD = Supply for PLL core
VDD1 = REF (0:2), X1, X2
VDD2 = PCICLK_F, PCICLK (0:6)
VDD3 = 48MHz0, 48MHz1
VDDL1 = IOAPIC (0:1)
VDDL2 = CPUCLK (0:3)
Ground Groups
GND = Ground for PLL core
GND1 = REF (0:2), X1, X2
GND2 = PCICLK_F, PCICLK (0:6)
GND3 = 48MHz0, 48MHz1
GNDL1 = IOAPIC (0:1)
GNDL2 = CPUCLK (0:3)
ICS reserves the right to make changes in the device data identified in this
publication without further notice. ICS advises its customers to obtain the
latest version of all device data to verify that any information being relied
upon by the customer is current and accurate.
PB
ICS9248-20
Pin Descriptions
Select Functions
Notes:
1. TCLK is a test clock driven on the X1 (crystal
in pin) input during test mode.
2. -0.5% modulation down spread from the
selected frequency.
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ICS9248-20
T echnical Pin Function Descriptions
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.
VDDL1,2
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 (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 (0:1)
This is a fixed frequency Clock output that is typically used to
drive Super I/O devices. Outputs 0 and 1 are defined as
48MHz.
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.
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 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.
SELECT 100/66.6MHz#
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).
PWR_DWN#
This is an asynchronous active Low Input pin used to Power
Down the device into a Low Power state by not removing the
power supply. The internal Clocks are disabled and the VCO
and Crystal are stopped. Powered 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
including SDRAM 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 affect
PCICLK_F nor any other outputs.
PB
ICS9248-20
Power Management
ICS9248-20 Power Management Requirements
Clock Enable Configuration
Full clock cycle timing is guaranteed at all times after the system has initially powered up except where noted. During power up
and power down operations using the PD# select pin will not cause clocks of a shorter or longer pulse than that of the running
clock. The first clock pulse coming out of a stopped clock condition may be slightly distorted due to clock network charging
circuitry. Board routing and signal loading may have a large impact on the initial clock distortion also.
Notes.
1. Clock on latency is defined from when the clock enable goes active to when the first valid clock comes out of the device.
2. Clock off latency is defined from when the clock enable goes inactive to when the last clock is driven low out of the device.
3. Power up latency is when PD# goes inactive (high) to when the first valid clocks are output by the device.
4. Power down has controlled clock counts applicable to CPUCLK, PCICLK only.
The REF and IOAPIC will be stopped independent of these.
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