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ICS9LPRS464

System Clock Chip for ATI RS/RD600 series chipsets using AMD CPUss

IDTTM/ICSTM

System Clock Chip for ATI RS/RD600 series chipsets using AMD CPUs

1377A—04/07/08

Fig. 1

Shared Pin Operation -

Input/Output Pins

The I/O pins designated by (input/output) on the ICS9LPRS464

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 5-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.

Figure 1 shows a means of implementing this function when a

switch or 2 pin header is used. With no jumper is installed the pin

will be pulled high. With the jumper in place the pin will be pulled

Via to

VDD

Clock trace to load

Series Term. Res.

Programming

Header

Via to Gnd

Device

Pad

2K

W

8.2K

W

low. If programmability is not necessary, than only a single resistor

is necessary. The programming resistors should be located close

to the series termination resistor to minimize the current loop area.

It is more important to locate the series termination resistor close

to the driver than the programming resistor.