6
ICS9147-09
Pins 2, 15, 46 and 47 on the ICS9147-09 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, (see
AC characteristics for timing values), the device changes
the mode of operations 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 devices
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).
Shared Pin Operation -
Input/Output Pins
The ICS9147-09 includes a production test verification
mode of operation. This requires that the FS2 and FS1 pins
be programmed to a logic high and the FS0 pin be
programmed to a logic low(see Shared Pin Operation
section). In this mode the device will output the following
frequencies.
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 devices X1 pin.
Test Mode Operation
Fig. 1
Pin
Frequency
REF, IOAPIC
REF
48MHz
REF/2
24MHz
REF/4
CPU, SDRAM
REF2
BUS
BSEL=1
REF/4
BUS
BSEL=0
REF/3