- 您現在的位置：買賣IC網 > PDF目錄363888 > W48S87-04 (IC WORKS INC) Spread Spectrum 3 DIMM Desktop Clock(寬頻譜3 DIMM桌上型PC機時鐘) PDF資料下載
參數資料
| 型號： | W48S87-04 |
| 廠商： | IC WORKS INC |
| 元件分類： | XO, clock |
| 英文描述： | Spread Spectrum 3 DIMM Desktop Clock(寬頻譜3 DIMM桌上型PC機時鐘) |
| 中文描述： | PROC SPECIFIC CLOCK GENERATOR, PDSO48 |
| 文件頁數： | 4/21頁 |
| 文件大小： | 200K |
| 代理商： | W48S87-04 |
W48S87-04
PRELIMINARY
4
Overview
The W48S87-04, a motherboard clock synthesizer, can pro-
vide either a 2.5V or 3.3V CPU clock swing, making it suitable
for a variety of CPU options. Twelve SDRAM clocks are pro-
vided in phase with the CPU clock outputs. This provides clock
support for up to three SDRAM DlMMs. Fixed output frequency
clocks are provided for other system functions.
Functional Description
I/O Pin Operation
Pins 2, 7, 8, 25, and 26 are dual-purpose l/O pins. Upon power-
up these pins act as logic inputs, allowing the determination of
assigned device functions. A short time after power-up, the
logic state of these pins is latched and the pins then become
clock outputs. This feature reduces device pin count by com-
bining clock outputs with input select pins.
An external 10-k
“
strapping
”
resistor is connected between
each l/O pin and ground or V
DD3
. Connection to ground sets a
latch to
“
0
”
, connection to V
DD3
sets a latch to
“
1
”
.
Figure 1
and
Figure 2
show two suggested methods for strapping resistor
connection.
Upon W48S87-04 power-up, the first 2 ms of operation is used
for input logic selection. During this period, these dual-purpose
I/O pins are three-stated, allowing the output strapping resistor
on each l/O pin to pull the pin and its associated capacitive
clock load to either a logic HIGH or LOW state. At the end of
the 2-ms period, the established logic 0 or 1 condition of each
l/O is pin is then latched. Next the output buffers are enabled,
which converts the l/O pins into operating clock outputs. The
2-ms timer is started when V
DD
reaches 2.0V. The input bits
can only be reset by turning V
DD
off and then back on again.
It should be noted that the strapping resistors have no signifi-
cant effect on clock output signal integrity. The drive imped-
ance of both clock outputs is <40
(nominal) which is minimal-
ly affected by the 10-k
strap to ground or V
DD
. As with the
series termination resistor, the output strapping resistor should
be placed as close to the l/O pin as possible in order to keep
the interconnecting trace short. The trace from the resistor to
ground or VDD should be kept less than two inches in length
to prevent system noise coupling during input logic sampling.
When the clock outputs are enabled following the 2-ms input
period, target (normal) output frequency is delivered assuming
that V
DD
has stabilized. If V
DD
has not yet reached full value,
output frequency initially may be below target but will increase
to target once V
DD
voltage has stabilized. In either case, a
short output clock cycle may be produced from the CPU clock
outputs when the outputs are enabled.
Power-on
Reset
Timer
Output Three-state
Data
Latch
Hold
Output
Low
Q
D
W48S87-04
V
DD
Clock Load
22
10 k
Output
Buffer
(Load Option 1)
10 k
(Load Option 0)
Output Strapping Resistor
Series Termination Resistor
Figure 1. Input Logic Selection Through Resistor Load Option
Power-on
Reset
Timer
Output Three-state
Data
Latch
Hold
Output
Low
Q
D
W48S87-04
V
DD
Clock Load
R
10 k
Output
Buffer
Output Strapping Resistor
Series Termination Resistor
Jumper Options
Figure 2. Input Logic Selection Through Jumper Option
Resistor Value R
39
33
Output
IOAPIC, SDRAM
All other clock outputs
相關PDF資料 |
PDF描述 |
|---|---|
| W48S87-72H | CPU System Clock Generator |
| W48S87 | Spread Spectrum 3 DIMM Desktop Clock |
| W48S87-72 | Desktop/Notebook Frequency Generator(桌上型電腦/筆記本電腦系統頻率發生器) |
| W49F002 | 256K X 8 CMOS FLASH MEMORY |
| W49F002U-12B | MB 32C 32#20 SKT RECP |
相關代理商/技術參數 |
參數描述 |
|---|---|
| W48S87-72 | 制造商:CYPRESS 制造商全稱:Cypress Semiconductor 功能描述:Desktop/Notebook Frequency Generator |
| W48S87-72H | 制造商:Cypress Semiconductor 功能描述:Logic and Timing, Clock Generation, Desktop/Notebook Frequency Generator |
| W48S87-72XT | 制造商:Rochester Electronics LLC 功能描述:- Tape and Reel |
| W49 | 制造商:CERAMATE 制造商全稱:CERAMATE 功能描述:3-Phase Motor Driver for CD-ROMs |
| W490 | 制造商:Pulse Electronics Corporation 功能描述:- Bulk |
發布緊急采購，3分鐘左右您將得到回復。