ics9248-99 Integrated Device Technology, ics9248-99 Datasheet - Page 6

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ics9248-99

Manufacturer Part Number
ics9248-99
Description
Frequency Generator & Integrated Buffers For Celeron & Pii/iii
Manufacturer
Integrated Device Technology
Datasheet
Shared Pin Operation -
Input/Output Pins
The I/O pins designated by (input/output) on the ICS9248-
99 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 the VDD (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.
0314C—09/18/03
ICS9248-99
Fig. 1
6
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).

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