ICS950223 Datasheet, PDF (22/24 Pages) Integrated Circuit Systems – Programmable Timing Control Hub for P4

Integrated
Circuit
Systems, Inc.
ICS950223
Shared Pin Operation -
Input/Output Pins
The I/O pins designated by (input/output) 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.
0496C—05/06/05
Programming
Header
Via to Gnd
Via to
VDD
2K W
Device
Pad
8.2K W
Clock trace to load
Series Term. Res.
Fig. 1
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