ICS9169C-271 Datasheet, PDF (3/8 Pages) Integrated Circuit Systems – Frequency Generator for Pentium™ Based Systems

ICS9169C-271
Shared Pin Operation -
Input/Output Pins
Shared Pin Operation - Input/Output Pins 5, 12, 13 and 32
on the ICS9169C-271 serve as dual signal functions to the
device. During initial power-up, they act as input pins. The
logic level (voltage) that is present on these pins at this time
is read and stored into a 4-bit internal data latch. At the end
of Power-On reset, (seeAC characteristics for timing values),
the device changes the mode of operation for these pins to
an output function. In this mode the pins produce the
specified buffered clocks to external loads.
To program (load) the internal configuration register for
these pins, a resistor is connected to either theVDD (logic 1)
power supply or the GND (logic 0) voltage potential. A 10
Kilohm(10K) resistor is used to provide both the solid CMOS
programming voltage needed during the power-up
programming period and to provide an insignificant load on
the output clock during the subsequent operating period.
Figs. 1 and 2 show the recommended means of implementing
this function. In Fig. 1 either one of the resistors is loaded
onto the board (selective stuffing) to configure the device’s
internal logic. Figs. 2a and b provide a single resistor loading
option where either solder spot tabs or a physical jumper
header may be used.
These figures illustrate the optimal PCB physical layout
options. These configuration resistors are of such a large
ohmic value that they do not effect the low impedance clock
signals. The layouts have been optimized to provide as little
impedance transition to the clock signal as possible, as it
passes through the programming resistor pad(s).
Test Mode Operation
The ICS9169C-271 includes a production test verification
mode of operation. This requires that the FS0 and FS1 pins
be programmed to a logic high and the FS2 pin be
programmed to a logic low(see Shared Pin Operation section).
In this mode the device will output the following
frequencies.
Pin
REF
48MHz
24MHz
CPU (1:12)
BUS (1:6)
BSEL=1
BSEL = 0
Frequency
REF
REF/2
REF/4
REF2
REF/4
REF/3
Note: REF is the frequency of either the crystal connected
between the devices X1and X2 or, in the case of a device
being driven by an external reference clock, the frequency
of the reference (or test) clock on the device’s X1 pin.
(Resistors are surface mount devices
shown schematically between 5.m. pads)
*use only one programming resistor
Fig. 1
3