Cypress W149H Datasheet

440BX AGPset Spread Spectrum Frequency Synthesizer

W149

Cypress Semiconductor Corporation

• 3901 North First Street • San Jose • CA 95134 • 408-943-2600
July 31, 2000 rev. *A

Features

• Maximized EMI suppression usi ng Cypress’s Spread
Spectrum Technology

• Single chip system frequency synthesizer for Intel

®

440BX AGPset

• Two copies of CPU output

• Six copies of PCI output

• One 48-MHz output for USB

• One 24-MHz output for SIO

• T wo buffered ref erence outputs

• One IO APIC out put

• Thirteen SDRAM outputs provide support for 3 DIMMs

• Spread Spectrum feature always enabl ed

•I

2

C™ interface for programming

• Po w er management control inputs

• Smooth CPU frequency swit ching from 66.8–124 MHz

Key Specifications

CPU Cycle-to-Cycle Jitter: .........................................250 ps

CPU to CPU Output Skew: . .. .. .................. .. .. ............. 175 ps

PCI to PCI Output Skew:.................................... ........ 500 ps

V

DDQ3

:.....................................................................3.3V±5%

V

DDQ2

:.....................................................................2.5V±5%

SDRAMIN to SDRAM0:12 Delay:..........................3.7 ns typ.

Table 1. Mode Input Table

[1]

Mode Pin 2

0 PCI_STOP#
1 REF0

T able 2. Pin Selectable Frequency

Input Address

CPU0:1

(MHz)

PCI_F, 1:5

(MHz)

Spread

%FS2 FS1 FS0

1 1 1 100 33.3 (CPU/3) –0.5
1 1 0 (Reserved)
1 0 1 100 33.3 (CPU/3) ±0.5
1 0 0 103 34.3 (CPU/3) –0.5
0 1 1 66.8 33.4 (CPU/2) –0.5
0 1 0 83.3 41.7 (CPU/2) –0.5
0 0 1 66.8 33.4 (C PU/2) ±0.5
0 0 0 124 41.3 (CPU/3) –0.5

Intel is a registered trademark of Intel Corporation. I2C is a trademark of Philips Corporation.

Notes:

1. Mode input latched at power-up.

2. Internal pull up resistors(*) should not be relied upon for setting I/O pins HIGH. Pin function with parentheses determined by MODE pin resistor strapping.

Logic Block Diagram

Pin Configuration

[2]

VDDQ3
REF0/(PCI_STOP#)

VDDQ2

CPU0

PCI_F/MODE

XT AL

PLL Ref Freq

PLL 1

X2

X1

REF1/FS2

VDDQ3

Stop

Clock

Control

PCI2
PCI3
PCI4

48MHz/FS0

24MHz/FS1

PLL2

÷2/÷3

OSC

VDDQ2

VDDQ3

IOAPIC

PCI5

I2C

SDATA

Logic

SCLK

I/O Pin
Control

SDRAM0:12

SDRAMIN

13

VDDQ3

PCI1

CPU1

÷2

VDDQ3

REF0/(PCI_STOP#)

GND

X1
X2

VDDQ3

PCI_F/MODE

PCI1
GND
PCI2
PCI3
PCI4
PCI5

VDDQ3

SDRAMIN

GND
SDRAM11
SDRAM10

VDDQ3
SDRAM9
SDRAM8

GND

SDA TA

SCLK

W149

VDDQ2
IOAPIC
REF1/FS2*
GND
CPU0
CPU1
VDDQ2
OE
SDRAM1 2
GND
SDRAM0
SDRAM1
VDDQ3
SDRAM2
SDRAM3
GND
SDRAM4
SDRAM5
VDDQ3
SDRAM6
SDRAM7
VDDQ3
48MHz/FS0*
24MHz/FS1*

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

I2C

{

W149

2

Pin Definitions

Pin Name Pin No. Pin Type Pin Description

CPU0:1 44, 43 O

CPU Clock Outputs:

See Tables 2 and 6 for detailed f requency informa tion. Output

voltage swing is controlled b y voltage applied to VDDQ2.

PCI1:5 8, 10, 11, 12,

13

O

PCI Clock Outputs 1 through 5:

These five PCI clock outputs are control led by
the PCI_STOP# control pin. Output voltage swing is controlled by voltage applied
to VDDQ3.

PCI_F/MODE 7 I/O

Fixed PCI Clock Output:

Frequency is set by the FS0:1 inputs or through serial
input interface, see Tables 2 and 6. This output is not affected by the PCI_STOP #
input. Upon po wer- up the mode inp ut will be latched, which will determine the f unc­tion of pin 2 , R E F0/(P C I_STOP #). Se e Table 1.

OE 41 I

Output Enable Input:

When brought LOW, all outputs are placed in a high-imped-

ance state. When brought HIGH, all clock outputs activate.

IOAPIC 47 O

IOAPIC Cloc k Output:

Provides 14.31 8-MHz fi xed frequency. The output voltage

swing is controlled by VDDQ2.

48MHz/FS0 26 I/O

48-MHz Output:

48 MHz is provi ded in normal oper ation. In stan dard system s, this
output can be used as the reference for t he Universal Serial Bus. Upon po wer-up,
FS0 input will be latched, which will set clock frequencies as described in Table 2.
This output does not have the Spread Spectrum feature.

24MHz/FS1 25 I/O

24-MHz Output:

24 MHz is provi ded in normal oper ation. In stan dard system s, this
output can be used as the cloc k input f or a Super I/O chip. Upon power-up FS1 inpu t
will be lat ched, wh ich wi ll set cloc k f req uencies as describ ed in Table 2. This outpu t
does not have the Spread Spectrum feature.

REF1/FS2 46 I/O

I/O Dual-Function REF1 and FS2 pin:

Upon power-up, FS2 input will be latched
which will set clock frequencies as described in Table 2. When an outp ut, this pin
provides a fixed clock signal equal in frequency to the reference signal provided at
the X1/X2 pins.

REF0/
(PCI_STOP#)

2I/O

Fixed 14.318-MHz Outpu t 0 or PCI_STOP# Pin:

Function is determined by the
MODE input. When set as an input, the PCI_STOP# input enabl es the PCI 1:5
outputs when HIGH and causes th em to remai n at logic 0 when LOW. The
PCI_STOP signal is latched on the rising edge of PCI_F. Its effects take place on
the next PCI_F clock cycle. When an output, this pin provides a fixed clock signal
equal in frequency to the reference signa l pr ovided at the X1/X2 pins.

SDRAMIN 15 I

Buffered Input Pin:

The signal provided to this input pin is buffered to 13 outputs

(SDRAM0:12).

SDRAM0:12 38, 37, 35,

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

20, 18, 17, 40

O

Buffered Outputs:

These thirteen dedicated outpu ts provide copies of the signal
provided at the SDRAMIN inpu t. The swing is set by VDDQ3, and they are deacti­vated when CLK_STOP# input is set LOW.

SCLK 24 I Clock pin for I

2

C circui try.

SDATA 23 I/O Data pi n for I

2

C circuitry.

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 connection or as an
external reference frequency input.

X2 5 I

Crystal Connection:

An input connection for an external 14.318-MHz crystal. If

using an external reference, thi s pin must be left unconnected.

VDDQ3 1, 6, 14, 19,

27, 30, 36

P

Po we r Connection:

Po wer supply for core logic, PLL circuitry, SDRAM outputs,

PCI outputs, reference outputs, 48-MHz output, and 24-MHz output. Conn ect to

3.3V supply.

VDDQ2 42, 48 P

Po wer Connection:

Po wer supply for IOAPIC and CPU0: 1 output b uff ers. Con nect

to 2.5V, or 3.3V.

GND 3, 9, 16, 22,

33, 39, 45

G

Ground Connections:

Connect all ground pins to the common system ground

plane.

W149

3

Overview

The W149 was developed as a single chip device to meet the
clocking needs of the Intel 440BX AGPset. In addition to the
typical output s prov id ed by st anda rd 100-MHz 440 BX A GPset
FTGs, the W149 adds a thirteen output buffer, supporting
SDRAM DIMM modules in con junction with the chipset.

Cypress proprietary spread spectrum frequency synthesis
technique is a f eature of the CPU and PCI outputs . This featur e
reduces the peak EMI measurements of not only the output
signals and t heir harmonics, but also of an y other cl ock sign als
that are properly synchronized to them.

Functional Description

I/O Pin Operation

Pins 7, 25, 26, 46 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 each pin is latched and the pins become clock
outputs. This feature reduces device pin count by combining
clock outputs with input select pins.

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

DD

. Connection to ground sets a

latch to “0”, connection to V

DD

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

Upon W149 power-up, the first 2 ms of operation is used for
input logic selection. During this period, the four I/O pins (7,
25, 26, 46) are three-stated, allowing the output strapping re­sistor on the l/O pins t o pull each pin and its ass ociated capac ­itive cloc k load to either a logi c HIGH or LO W st at e. At the end
of the 2-ms period, the establi shed logic “0” or “1” condition of
the l/O pin is latched. Next the output buffer is enabled, con­verting the l/O p ins i nto oper a ting c loc k ou tputs . The 2-ms tim­er starts 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 clock out put is <40Ω (nominal), which is mini ma ll y af­fected by the 10-kΩ strap to ground or V

DD

. As wi th 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 V

DD

should be ke pt less t han tw o i nches i n lengt h to

prevent system noise coupling during input logic sampling.
When the clock outputs are enabled following the 2-ms input

period, the specified output frequency is delivered on the pin,
assuming that V

DD

has stabilized. If VDD has not yet reached
full va lue, output frequency initi ally ma y be belo w target b ut 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

QD

W149

V

DD

Clock Load

10 k

Ω

Output
Buffer

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10 k

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Output
Low

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Figure 1. Input Logic Selection Through Resistor Load Option

Power-on
Reset
Timer

Output Three-state

Data

Latch

Hold

QD

W149

V

DD

Clock Load

R

10 k

Ω

Output
Buffer

Output
Low

Output Strapping Resistor

Series Termination Resistor

Jumper Options

Resistor Value R

Figure 2. Input Logic Selection Through Jumper Option

W149

4

Spread Sp ectrum C locki n g

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 shown in Figure 3, a harmonic of a modulated clock has a
much low er amplitude t han that of an un modulated si gnal. The
reduction in amplitude is dependent on the harmonic number
and the frequency deviation or spread. The equation for the
reduction is:

dB = 6.5 + 9*log10(P) + 9*log10(F)

Where 3 is the percentage of deviation and ) is the frequency
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 Spectrum
Clock Gener ation f or the Redu ct ion of Radiat ed Emiss ions” by
Bush, Fessler, and Hardin produces the maximum reduction
in the amplitude of radiated electromagnetic emissions. The
deviati on select ed f or this chip is either –0.5% or ±0.5% of the
selected frequency. Figure 4 details the Cypress spreading
pattern. Cypress does offer options with more spread and
greater EMI r eduction. Cont act your local Sal es represen tativ e
for details on these devices.

Spread Spectrum clocking cannot be deactivated on the
W149.

Figure 3. Clock Harmonic with and without SSCG Modul ati on Frequency Domain Representation

SSFTG Typical Clock

Frequency Span (MHz)

Amplitude (dB)

Center Spread

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

Figure 4. Typical Modulation Profile

W149

5

Serial Data Interface

The W149 features a two-pin, serial data interf ace that can b e
used to configure internal register settings that control partic­ular de vice func tions. Upon power -up , the W149 i nitiali zes wit h
default register settings, therefore the use of this serial data
interface is optional. The serial interface is write-only (to the
clock chi p) and is t he dedica ted func tion of de vice pins SD ATA
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, if any are required. The interface
can also be used durin g system operation for power manage­ment functions. Tab l e 3 summarizes the control functions of
the serial data interface.

Operation

Data is written to the W149 in eleven bytes of eight bits each.
Bytes are written in the order sho w n in Table 4.

Table 3. Serial Data Interface Contr ol Functions Summary

Control Function Description Common Application

Clock Output Disable Any individual clock output(s) can be disabled.

Disabled out puts are actively held LOW .

Unused outputs are disabled to reduce EMI
and system power. Examples are clock
outputs to unus ed PCI slots.

CPU Clock Frequency
Selection

Provides CPU/PCI fr equency selections throug h
software. Frequency is changed in a smooth and
controlled fashion.

For alternate microprocessors and power
management options. Smooth frequency
transition allows CPU frequency change

under normal system operation.
Output Three-st ate Puts clock out put into a high-impedance st ate. Production PCB testi ng.
(Reserved) Reserved functi on for future dev ice revision or

production device testing.

No user application. Register bit must be

written as 0.

Table 4. Byte Writing Sequence

Byte

Sequence Byte Name Bit Sequence Byte Description

1 Slave Address 11010010 Commands the W149 to accept the bi ts in Data Bytes 0–6 for internal

register co nfigurati on. Since othe r devi ces may exist on the same com­mon serial data bus, it is ne cessary to hav e a specific slav e address f or
each potential receiver. The slave recei ver address f or the W149 is

11010010. Regist er setting wi ll not be made if the Slav e Addr ess is not
correct (or is for an alternate slave receiver).

2 Command Code Don’t Care Unused by the W149, therefore bit values are ignored (“Don’t Care”).

This byte must be included in the data write sequence to maintain prop ­er byte allocation. The Command Code Byte is part of the standard
serial communi ca tion protoc ol and ma y be use d wh en writi ng t o a noth­er addressed slave receiver on the serial data bus.

3 Byte Count Don’t Care Un used by the W149, therefore bit values are ignored (“Don’t Care”).

This byte must be included in the data write sequence to maintain prop ­er byte allocation. The Byte Count Byte is part of the standard serial
communication protocol and may be used when writing to another ad­dressed slave receiver on the serial data bus.

4 D ata Byte 0 Refer to Table 5 The data bit s in Data Bytes 0–7 s et internal W149 register s that c ontrol

device operation. The data bits are only accepted when the Address
Byte bit seq uence is 11010010, as noted above. For description of bit
control f unctions, refer to Table 5, Data Byte Serial Configuration Map.

5 D ata Byte 1
6 D ata Byte 2
7 D ata Byte 3
8 D ata Byte 4

9 D ata Byte 5
10 Data Byte 6
11 Data Byte 7