W164G Cypress Semiconductor Corp., W164G Datasheet - Page 3

• Manufacturer Part Number: W164G
• Description: Spread Spectrum Desktop / Notebook System Frequency Generator
• Manufacturer: Cypress Semiconductor Corp.

Serial Data Interface
The W164 features a two-pin, serial data interface that can be
used to configure internal register settings that control partic-
ular device functions. Upon power-up, the W164 initializes
with default register settings. Therefore, the use of this serial
data interface is optional. The serial interface is write-only (to
the clock chip) and is the dedicated function of device pins
SDATA and SCLOCK. In motherboard applications, SDATA
and SCLOCK are typically driven by two logic outputs of the
Table 2. Serial Data Interface Control Functions Summary
Document #: 38-07169 Rev. *A
Control Function
Clock Output Disable
CPU Clock Frequency
Selection
Output Three-state
Test Mode
(Reserved)
Power-on
Reset
Timer
Power-on
Reset
Timer
W164
W164
Description
Any individual clock output(s) can be disabled. Dis-
abled outputs are actively held LOW.
Provides CPU/PCI frequency selections beyond the
100- and 66.6-MHz selections that are provided by
the SEL100/66# pin. Frequency is changed in a
smooth and controlled fashion.
Puts all clock outputs into a high-impedance state. Production PCB testing.
All clock outputs toggle in relation to X1 input, inter-
nal PLL is bypassed. Refer to Table 4.
Reserved function for future device revision or pro-
duction device testing.
Figure 1. Input Logic Selection Through Resistor Load Option
Output Three-state
Figure 2. Input Logic Selection Through Jumper Option
Output Three-state
Output
Buffer
Q
Output
Buffer
Latch
Q
Data
Latch
Data
D
Hold
Output
Low
D
Hold
Output
Low
(Load Option 1)
(Load Option 0)
10 k
chipset. Clock device register changes are normally made
upon system initialization, if required. The interface can also
be used during system operation for power management func-
tions. Table 2 summarizes the control functions of the serial
data interface.
Operation
Data is written to the W164 in ten bytes of eight bits each.
Bytes are written in the order shown in Table 3.
Jumper Options
10 k
10 k
V
DD
Resistor Value R
V
DD
Common Application
Unused outputs are disabled to reduce EMI
and system power. Examples are clock out-
puts to unused PCI slots.
For alternate microprocessors and power
management options. Smooth frequency tran-
sition allows CPU frequency change under
normal system operation.
Production PCB testing.
No user application. Register bit must be writ-
ten as 0.
R
Output Strapping Resistor
Output Strapping Resistor
Series Termination Resistor
Series Termination Resistor
Clock Load
Clock Load
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W164