7

ICS9250-18

Third party brands and names are the property of their respective owners.

Shared Pin Operation -

Input/Output Pins

Fig. 1

The I/O pins designated by (input/output) on the ICS9250-

18 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).