Cypress W48S87-04H Datasheet

PRELIMINARY

Spread Spectrum 3 DIMM Desktop Clock

W48S87-04

Cypress Semiconductor Corporation

• 3901 North First Street • San Jose • CA 95134 • 408-943-2600
October 19, 1999, rev. **

Features

• Outputs
—4 CPU Clock (2.5V or 3.3V, 50 to 83.3 MHz)
—7 PCI (3.3V)
—1 48- MHz for USB (3.3V)
—1 24-MHz for Super I/O (3.3V)
—2 REF (3.3V)
—1 IOAPIC (2.5V or 3.3V)
—12 SDRAM

• Serial data interface provides additional frequency

selection, individual clock output disable, and other
functions

• Smooth transition supports dynamic frequency

assignment

• Frequency selection not affected during power

down/up cycle

• Supports a variety of power-saving options

• 3.3V operation

• Av ail able in 48-pin SSOP (300 mils)

Key Specifications

±0.5% Spread Spectrum Modulation: .........................±0.5%

Jitter (C y c le -to-Cyc l e ):... ... ...................... .. ... .............. ..2 5 0 ps

Duty Cyc l e: ...... .................................... ... .. ................. 45-55 %

CPU-P C I S kew:.... .................................... ... .. ...........1 to 4 ns

PCI-PC I or CPU-CP U S kew: . .. ....... ... .. ...................... ..2 5 0 ps

Notes:

1. Additional frequency selections provided by serial data interface; refer to

Table 5

on page 10.

2. Signal names in parenthesis denotes function is selectable through mode pin register strapping.

T able 1. Pin Selectable Frequency

[1]

Input Address

CPU, SDRAM
Clocks (MHz)

PCI Clocks

(MHz)FS2 FS1 FS0

0 0 0 50.0 25.0
0 0 1 75.0 32.0
0 1 0 83.3 41.65
0 1 1 68.5 34.25
1 0 0 55.0 27.5
1 0 1 75.0 37.5
1 1 0 60.0 30.0
1 1 1 66.8 33.4

Block Diagram

Pin Configuration

[2]

VDD1

IOAPIC

VDD3
SDRAM0:11

PCI_F/FS1
PCI0/FS2

XTAL OSC

PLL Ref

PLL1

X2

X1

REF1(CPU_ST OP#)

Stop

Clock

Cntrl

PCI1:4

PWR_DWN#

Power Down
Control

PCI5(PWR_DWN#)

48MHZ/FS0
24MHZ/MODE

PLL2

Serial Port

SCLOCK

SDA TA

Device

CPU_STOP#

Control

CPU3.3#_2.5

CPU Clock
Mode Control

÷4

÷2

I/O

I/O

VDD1

MODE

4

I/O

I/O

VDD2

12

CPU0:3

4

VDDL2

÷2

VDDL1

MODE

I/O

REF0/CPU3.3#_2.5

Freq

Select

FS0
FS1
FS2

Freq

VDD1

REF0/CPU3.3#_2.5

GND

X1
X2

VDD2

PCI_F/FS1

PCI0/FS2

GND
PCI1
PCI2
PCI3
PCI4

VDD2

PCI5(PWR_DWN#)

GND
SDRAM11
SDRAM10

VDD3
SDRAM9
SDRAM8

GND

SDATA

SCLOCK

W48S87-04

VDDL1
IOAPIC
REF1(CPU_STOP#)
GND
CPU0
CPU1
VDDL2
CPU2
CPU3
GND
SDRAM0
SDRAM1
VDD3
SDRAM2
SDRAM3
GND
SDRAM4
SDRAM5
VDD3
SDRAM6
SDRAM7
GND
48MHZ/FS0
24MHZ/MODE

48
47
46
45
44
43
42
41
40
39
38
37
36
35
34
33
32
31
30
29
28
27
26
25

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24

W48S87-04

PRELIMINARY

2

Pin Definitions

Pin Name

Pin
No.

Pin

Type Pin Description

CPU0:3 44, 43, 41, 40O

CPU Clock Outputs 0 through 3:

These four CPU clock output s are controll ed
by the CPU_STOP# control pi n. Output voltage swing is controlled by voltage
applied to VDDL2 and output characteristics are adj usted by input
CPU3.3#_2.5.

PCI_F/FS1 7 I/O

Fixed PCI Cloc k Output and Frequency Selection Bit 1:

As an output, this
pin works in conjunction with PCI0:5. Output vol tage swing is control led by
voltage applied to VDD2.

When an input, this pin functions as part of the frequency selection address.
The value of FS0:2 determines the po wer-up def ault freque ncy of devi ce output
clocks as per the Table 1, “Pin Selectable Frequency” on page 1.

PCI0/FS2 8 I/O

PCI Bus Clock Output 0 and Frequency Selection Bit 2:

As an output, this
pin works in conjunction with PCI1:5 and PCI_F. Output voltage swing is con­trolled by voltage applied to VDD2.

When an input, this pin functions as part of the frequency selection address.
The value of FS0:2 determines the po wer-up def ault freque ncy of devi ce output
clocks as per the Table 1, “Pin Selectable Frequency” on page 1.

PCI1:4 10, 11, 12, 13O

PCI Bus Clock Outputs 1 through 4:

Output volt age swing is controlled by

voltage applied to VDD2.

PCI5(PWR_DWN#) 15 I/O

PCI Bus Cloc k Output 5 o r Power- Down Control:

As an output, this pin works
in conjunction wi th PCI0:4 and PCI_F. Output voltage s wing is controlled by
voltage applied to VDD2.

If progr ammed as an input ( ref er to MO DE pin descript ion), this pi n is used f or
power-down control. When LOW, the device goes into a low-power standby
condition. All outputs are activel y held LOW while in power-down. CPU,
SDRAM, and PCI clock out puts ar e stopped LO W after com pleting a f ull cl ock
cycle (2–4 CPU cloc k cycle late ncy). When b rought HIGH, CPU , SDRAM, an d
PCI outputs start with a full clock cycle at full operating frequency (3 ms max­imum latency).

SDRAM0:11 38, 37, 35,

34, 32, 31,
29, 28, 21,

20, 18, 17

O

SDRAM Clock Outputs 0 through 11:

These twelve SDRAM clock outputs
run synchronous to the CPU clo ck outputs. Output vol tage swing is controlled
by volt age applied to VDD3.

IOAPIC 47 O

I/O APIC Clock Output:

Provides 14.31 8-MHz fixed frequency. The output

voltage swing is controlled by VDDL1.

48MHZ/FS0 26 I/O

48-MHz Output and Frequency Selection Bit 0:

Fixed clock output that de­fault s to 48 MHz f oll o wing de vice po w er-up . Output voltage swing is controll ed
by volt age applied to VDD1.

When an input, this pin functions as part of the frequency selection address.
The value of FS0:2 determines the po wer-up def ault freque ncy of devi ce output
clocks as per the Table 1, “Pin Selectable Frequency” on page 1.

24MHZ/MODE 25 I/O

24-MHz Output and Mode Contr ol Input:

Fixed cloc k output that defaults to
24 MHz following device power-up. Output voltage swing is controlled by volt­age applied to VDD1.

When an input, this pin i s used for pin programming selection . It determines
the functio ns for pins 15 and 46:

MODE Pin 15 Pin 46

0 PWR_DWN# (input) CPU_STOP# (input)
1 PCI5 (output) REF1 (output)

W48S87-04

PRELIMINARY

3

REF0/CPU3.3#_2.5 2 I/O

Fixed 14.318-MHz Output 0 and CPU Output Voltage Swing Selection
Input:

As an output, this pin is used for various sy stem applications. Output
voltage swing is controlled b y v olt age appli ed to VDD1. REF0 is stro nger than
REF1 and should be used for driving ISA slots.

When an input, thi s pin selects the CPU clock output buff er charac teristics th at
are optimiz ed for either 3.3V or 2.5V ope ration.

CPU3.3#_2.5 VDDQ2 Voltage (CPU0:3 Swing)

03.3V

12.5V

This input a djusts CPU clock output impedance so that a nominal 20Ω output
impedance is maintained. This eliminates or reduces the need to adjust ext er­nal clock t uning components when changing VDDL2 v oltage. CPU cloc k phase
is also adjusted so that both CPU and SDRAM and CPU-to-PCI clock ske w is
maintained over the two VDDL2 voltage options. This input does not adjust
IOAPIC cl ock output charact e ri stics.

REF1(CPU_Stop#) 46 I/O

Fixed 14.318-MHz Output 0 or CPU Clock Output Stop Control:

Used for
various syst em applications. O utput voltage sw ing is controlled by voltage ap­plied to VDD1. REF0 i s stronger than REF 1 and shoul d be used f or driving ISA
slots.

If progr ammed as an input ( ref er to MO DE pin descript ion), this pi n is used f or
stopping the CPU clock outputs. When brought LOW, clock outputs CPU0:3
are stopped LOW after completing a full clock cycle (2–3 CPU clock l atency).
When brought HI GH, clock outputs CPU0:3 are starting beginning with a full
clock cy c l e (2–3 CPU clock latency).

X1 4 I

Crystal Connection or External Reference Frequency Input:

This pin has
dual functions. It can be used as an external 14.318-MHz crystal connect ion
or as an external reference frequency input.

X2 5 I

Crystal Connection :

An input conn ection f or an ex ternal 14. 318-MHz crystal.

If using an external r eference, this pin must be left unconnected.

SDATA 23 I

Serial Data Input:

Data input for Serial Dat a In terface. Re fer to Serial Data

Interface section that follows.

SCLOCK 24 I

Serial Clock Input:

Clock input for Serial Data Interface. Refer to Serial Data

Interface section that follows.

VDD1 1 P

Powe r Connect ion:

Power supply for crystal oscillator and REF0 :1 output

buffers. Connected to 3.3V suppl y.

VDD2 6,14 P

Powe r Connection:

Po wer supply for PCI clock output buffers. Connected to

3.3V supply.

VDDL1 48 P

Powe r Connection:

Po wer supply f or IOAPIC out put buffer . Connected to 2.5V

or 3.3V supply.

VDDL2 42 P

Powe r Connect ion:

Po wer supply for CPU clock output b u ff ers. Connect ed to

2.5V or 3.3V supply.

VDD3 19, 30, 36 P

Powe r Connection:

Pow er supply f or SDRAM clock o utput buff ers. Conn ected

to 3.3V supply.

GND 3, 9, 16, 22,

27, 33, 39,

45

G

Ground Connection:

Connect all ground pin s to the comm on system gr ound

plane.

Pin Definitions

(continued)

Pin Name

Pin
No.

Pin

Type Pin Description

W48S87-04

PRELIMINARY

4

Overview

The W48S87-04, a motherboard clock synthesizer, can pro­vide eith er a 2.5V or 3.3 V CPU clock swing, making i t suitabl e
for a variety of CPU options. Twelve SDRAM clocks are pro­vided in phase wit h the CPU cloc k outputs . This pro vides clock
support for up to three SDRAM DlMMs. Fixed outp ut frequency
clocks are pr ovided for oth er system functions.

Functional Description

I/O Pin Operation

Pins 2, 7, 8, 25, and 26 ar e dual-purpose l/O pins . Upon power­up these pins act as log ic in puts, all owing the det erminatio n 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 com­bining cloc k outputs with input selec t pi ns.

An external 10-kΩ “strapping” resistor is connected between
each l/O pin and ground or V

DD3

. Connection to gr ound s ets a

latch to “0”, connection to V

DD3

sets a latch to “1”. Figure 1 an d
Figure 2 show two suggested methods for strapping resistor
connection.

Upon W48S87-04 pow er-up , the first 2 ms of op eration is use d
for inpu t logic selecti on. During this period, these dual-purpose

I/O pins are three-state d, allo wing the ou tput str apping re sistor
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 establi shed 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 signifi­cant effect on clock output signal integrity. The drive imped­ance of both cloc k output s is <40Ω (nominal) whic h is minimal ­ly affected by the 10-kΩ strap to ground or V

DD

. As with the
series termination resist or, the output strapping res istor 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 duri ng input logic sampling.

When the clock out puts are enabled following the 2-ms input
period, target ( normal) output f requenc y is deliv ered a ssuming
that V

DD

has stabilized. If VDD has not yet reached full value,
output frequency in iti ally ma y be below t arget b ut wil l in crease
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

QD

W48S87-04

V

DD

Clock Load

22

Ω

10 k

Ω

Output
Buffer

(Load O ption 1)

10 k

Ω

(Load O ption 0)

Output
Low

Output Strapping Resistor

Series Termination Resistor

Figure 1. Input Logic Selection Thr ough Resistor Load Option

Power-on
Reset
Timer

Output Three-state

Data

Latch

Hold

QD

W48S87-04

V

DD

Clock Load

R

10 k

Ω

Output
Buffer

Output
Low

Output Strapping Resistor

Series Termination Resistor

Jumper Options

Figure 2. Input Logic Selection Thr ough Jumper Option

Resistor Value R

39

Ω

33

Ω

Output

IOAPIC, SDRAM
All other clock outputs

W48S87-04

PRELIMINARY

5

CPU/PCI Freq uency Selection

CPU frequency is selected with I/O pins 26, 7, and 8
(48MHz/FS0, PCI_F/FS1, and PCI0/FS2, respectively). Refer
to Table 1 for CPU/PCI frequency programming infor mation.
Additional fr equency sel ect ions ar e av ailab l e throug h the seri­al data interf ace. Refer to Table 5 on page 10.

Output Buffer Configuration

Clock Output s

All clock outputs are designed to drive serial terminated clock
lines. T he W48S87-04 out put s are CMOS -type , whic h prov ide
rail-to-rail output swing. To accommodate the limited voltage
swing required by some processors, the output buffers of
CPU0:3 use a special VDDL2 power supply pin that can be
tied to 2.5V nominal.

Crystal Oscillator

The W48S87-04 requires one input ref erence clock to synthe­size all output frequencies. The reference clock can be either
an externall y gener ated clo c k signal or the cl ock gen er ated by

the internal crystal oscillator. When using an ex ternal clock
signal, pin X1 is us ed as the cloc k input and pi n X2 is left open .
The input threshold voltage of pin X1 is V

DD

/2.

The internal crystal oscillator is used in conjunction with a
quartz crystal connected t o de vi ce pins X 1 and X2 . Th is f orms
a parallel resonant crystal oscillator circuit. The W48S87-04
incorporates the necessary f ee dback r esist or and crystal load
capacitors . Inclu ding typi cal st ra y ci rcuit capac itanc e, the total
load presented to the crystal is approximately 20 pF. For opti­mum frequency accuracy without the addition of external ca­pacitors, a parallel-resonant mode crystal specifying a load of
20 pF should be used. This will typically yield reference fre­quency accuracies within ±100 ppm.

Dual Supply Voltage Operation

The W48S87-04 is designed for dual power supply operation.
Supply pins VDD1, VDD2, and VDD3 a re co nnected t o a 3.3V
supply and supply power to th e internal core circuit and to the
clock output buffers, except for outputs CPU0:3 and IOAPIC.
Supply pins VDDL1 and VDDL2 ma y be connected to either a

2.5V or 3.3V supply.

W48S87-04

PRELIMINARY

6

Spread Sp ectrum Generator

The device generates a clock that is frequency modulated in
order to increase the bandwidth that it occu pies. By increas ing
the bandwidth of the fundamental and its harmonics, the am­plitudes of the radiated electromagnetic emissions are re­duced. This effect is depicted in Figure 3.

As depicted in Figure 3, a harmonic of a modulated clock has
a much lower amplitude than that of an unmodulated signal.
The reduction in am plitude is dependen t on the harmonic num­ber and the frequency deviation or spread. The equation for
the reductio n is

dB = 6.5 + 9*log

10

(P) + 9*log10(F)

Where P is the per cent age of de viat i on and F is the freq uency
in MHz where the reduction is measured.

The output clock is modulated with a waveform depicted in
Figure 4. This waveform, as discussed in “Spread Spect rum
Clock Generation f or the Reducti on of Radiated Emissio ns” by
Bush, Fessler, and Hardin produces the maximum reduction
in the amplitude of radiated electromagnetic emissions. The
deviati on select ed fo r th is chip is ±0. 5% of the ce nter frequen ­cy. Figure 4 details the Cypress spreading pattern. Cypress
does offer options with more spread and greater EMI reduc­tion. Contact your local Sales representative for details on
these devices.

Spread Spectrum clocking is activated or deactivated by se­lecting the appropriate v al ues fo r bits 1–0 in data byte 0 of the
I

2

C data stream. Refer to Table 4 for more detail s.

Figure 3. Clock Harmonic with and without SSCG Modulation Frequency Domain Representation

SSFTG Typical Clock

Frequency Span (MHz)

+1.0

-SS%

+SS%

Amplitude (dB)

5dB/di v

Figure 4. Typica l Modulation Profile

MAX (+.0.5%)

MIN. (–0.5%)

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

FREQUENCY

W48S87-04

PRELIMINARY

7

Serial Data Interface

The W48S87-04 features a two-pin, serial data interface that
can be used to configure internal register settings that control
particular device functions. Upon power-up, the W48S87-04
initiali zes with defaul t registe r setti ngs, t herefo re the use of this
serial data interface is optional. The serial interface is write­only (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 chipset. Clock device register changes are normally
made upon system initialization, i f any are required. The inter­face can also be us ed during system oper ation f or power man­agement functions. Table 2 summarizes the control functions
of the serial data interface.

Operation

Data is written to the W48S87-04 in ten bytes of eight bits
each. Bytes are written in the or der shown in Table 3.

T able 2. Serial Data Interface Control Func ti ons Sum mary

Control Function Description Common Application

Clock Output Disable Any indivi dual clock output(s) can be disabled. Dis-

abled outputs ar e actively held LO W.

Unused outputs are di sabled to reduce EMI
and system power. Examples are clock out­puts to unused SDRAM DIMM socket or PCI
slot.

CPU Clock Frequency
Selection

Provides CPU/PCI fr equency selections be yond the
50- and 66.8-MHz selections that are provided by
the FS0:2 power- on defaul t selection. Frequ ency is
changed in a smooth and controlled fashion.

For alternate CPU devi ces, and power man­agement options. Smooth frequency transi­tion allows CPU fr equency ch ange un der nor-

mal system operati on.
Output Three-state Puts all clock outputs into a high-impedance state. Production PCB testing.
Test Mode All clock outputs toggle in relat ion with X1 input,

internal PLL is bypassed. Refer to Tabl e 4.

Production PCB testing.

(Reserved) Reserved functio n for future de vice revisi on or pro-

duc tion dev ice tes t i ng.

No user application . Regist er bit must be wri t-

ten as 0.

Table 3. Byte Writing Sequence

Byte Sequence Byte Name Bit Sequence Byte Description

1 Slave Address 11010010 Commands the W48S87-04 to accept the bits in Data Byte s 0 –6 f or

internal register configuration. Since other devices may exist on the
same common serial data bus, it is necessary to have a specific slave
address for each potential receiver. The slave receiver address for the
W48S87-04 is 11010010. Regi ster set ting will not be made if the Sla v e
Add r ess is n ot corr ect (or is for an alter nat e slave rec e i ve r).

2 Command

Code

Don’t Care Unused by the W48S87-04, therefore bit values are ignored (“don’t

care”). This b yte must be included in the data write se quence to mai ntain
proper byte all ocation. The Command Code Byt e is part of the standar d
serial communicat ion protocol and may be us ed when writing to another
addressed slave receiver on the serial data bus.

3 Byte Count Don’t Care Unused by the W48S87-04, therefore bit values are ignored (“don’t

care”). This b yte must be included in the data write se quence to mai ntain
proper byte allo cation. The Byte Count Byt e is part of the standard serial
communication protocol and may be used when writin g to anot her ad­dressed slave receiver on the serial data bus.

4 Data Byte 0 Refer to Ta ble 4 The data bits in these bytes set internal W48S87-04 registe rs that con-

trol dev ice oper ation. Th e data bits are only a ccepted when the Addr ess
Byte bit sequence is 11010010, as noted above. For description of bit
control functions, refer to Table 4, Data Byte Serial Configurati on M ap.

5 Data Byte 1
6 Data Byte 2
7 Data Byte 3
8 Data Byte 4
9 Data Byte 5

10 Data Byte 6