7

ICS9147-12

Pins 1 and 2 on the ICS9147-12 serves as dual signal

functions to the device. During initial power-up, it acts as an

input pin. The logic level (voltage) that is present on this pin

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 this pin to an output function. In this mode the pin

produces the specified buffered clocks to external loads.

To program (load) the internal configuration register for this

pin, 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.

Shared Pin Operation -

Input/Output Pins

Fig. 1

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).