ICS951413 Datasheet, PDF (21/23 Pages) Integrated Circuit Systems – Programmable System Clock Chip for ATI RS400 P4-based Systems

Integrated
Circuit
Systems, Inc.
ICS951413
Shared Pin Operation -
Input/Output Pins
The I/O pins designated by (input/output) on the ICS951416
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 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.
0929C—03/07/05
Programming
Header
Via to Gnd
Via to
VDD
2K W
Device
Pad
8.2K W
Clock trace to load
Series Term. Res.
Fig. 1
21