ICS9147-14 查看數據表（PDF） - Integrated Circuit Systems

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ICS9147-14

Frequency Generator & Integrated Buffers for PENTIUM/Pro™

Integrated Circuit Systems 

ICS9147 - 14

Shared Pin Operation -

Input/Output Pins

Pins 7, 8 and 26 on the ICS9147-14 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.

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).

Fig. 1

5

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