PRELIMINARY
Output Strapping Resistor
Series Termination Resistor
W209C
Power-on
Reset
Timer
Clock Load
Output
Buffer
Output Three-state
Q
W209C
Hold
Output
Low
D
10kΩ
Data
Latch
Figure 1. Input Logic Selection Through Resistor Load Option
Overview
The W209C is a highly integrated frequency timing generator,
supplying all the required clock sources for an Intel® architec-
ture platform using graphics integrated core logic.
Functional Description
I/O Pin Operation
Pin # 1, 10, 11, 12, 22, and 23 are dual-purpose l/O pins. Upon
power-up the pin acts as a logic input. An external 10-kΩ strap-
ping resistor should be used.
Figure 1
shows a suggested
method for strapping resistor connections.
After 2 ms, the pin becomes an output. Assuming the power
supply has stabilized by then, the specified output frequency
10 ns
20 ns
is delivered on the pins. If the power supply has not yet
reached full value, output frequency initially may be below tar-
get, but will increase to target once supply voltage has stabi-
lized. In either case, a short output clock cycle may be pro-
duced from the CPU clock outputs when the outputs are
enabled.
Offsets Among Clock Signal Groups
Figure 2
and
Figure 3
represent the phase relationship among
the different groups of clock outputs from W209C when it is
providing a 66-MHz CPU clock and a 100-MHz CPU clock,
respectively. It should be noted that when CPU clock is oper-
ating at 100 MHz, CPU clock output is 180 degrees out of
phase with SDRAM clock outputs.
0 ns
30 ns
40 ns
CPU 100 Period
CPU 66-MHz
SDRAM 100 Period
SDRAM 100-MHz
3V66 66-MHz
PCI 33-MHz
REF 14.318-MHz
USB 48-MHz
APIC
Hub-PC
Figure 2. Group Offset Waveforms (66-MHz CPU Clock, 100-MHz SDRAM Clock)
Document #: 38-07171 Rev. *A
Page 3 of 16
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