ChipFind - документация

Электронный компонент: W156C

Скачать:  PDF   ZIP
PRELIMINARY
Spread Spectrum FTG for VIA MVP4
W156C
Cypress Semiconductor Corporation
3901 North First Street
San Jose
CA 95134
408-943-2600
November 17, 1999, rev. **
Features
Maximized EMI suppression using Cypress's Spread
Spectrum technology
Single-chip implementation
Four copies of CPU output
Six copies of PCI output
One 48-MHz output for USB
One 24-MHz output for SIO
Two buffered reference outputs
Thirteen SDRAM outputs provide support for 3 DIMMs
Supports frequencies up to 124 MHz
I
2
CTM interface for programming
Power management control inputs
Key Specifications
CPU Cycle-to-Cycle Jitter: .......................................... 250 ps
CPU to CPU Output Skew: ......................................... 300 ps
CPU to PCI Output Skew: .................................. 1.5 to 4.0 ns
PCI to PCI Output Skew: ............................................ 500 ps
V
DDQ3
= V
DDQ_CPU
= .............................................. 3.3V5%
SDRAMIN to SDRAM0:11 Delay: ..........................4.7 ns typ.
SDRAM0:11 (leads) to SDRAM_F Skew ...............0.4 ns typ.
Table 1. Mode Input Table
Mode
Pin 3
0
PCI_STOP#
1
REF0
Table 2. Pin Selectable Frequency
Input Address
CPU, SDRAM
(MHz)
PCI_F, 1:5
(MHz)
FS3
FS2
FS1
FS0
1
1
1
1
60
30 (CPU/2)
1
1
1
0
66.8
33.4 (CPU/2)
1
1
0
1
70
35 (CPU/2)
1
1
0
0
75
25 (CPU/3)
1
0
1
1
97
32.3 (CPU/3)
1
0
1
0
83.3
27.7 (CPU/3)
1
0
0
1
95.25
31.75 (CPU/3)
1
0
0
0
100
33.3 (CPU/3)
0
1
1
1
75
37.5 (CPU/2)
0
1
1
0
96.2
32.0 (CPU/3)
0
1
0
1
83.3
41.7 (CPU/2)
0
1
0
0
105
35 (CPU/3)
0
0
1
1
110
36.7 (CPU/3)
0
0
1
0
115
38.3 (CPU/3)
0
0
0
1
120
40 (CPU/3)
0
0
0
0
124
41.3 (CPU/3)
I
2
C is a trademark of Philips Corporation.
Logic Block Diagram
Pin Configuration
[1, 2]
REF0/(PCI_STOP#)
CPU1:3
PCI_F/MODE
XTAL
PLL Ref Freq
PLL 1
X2
X1
REF1/FS2
Stop
Clock
Control
Stop
Clock
Control
PCI2
PCI3
PCI4
48MHz/FS0
24MHz/FS1
PLL2
2,3
OSC
CLK_STOP#
PCI5
I
2
C
SDATA
Logic
SCLK
I/O Pin
Control
SDRAM0:11
SDRAMIN
12
VDDQ3
PCI1/FS3
Stop
Clock
Control
CPU_F
2
SDRAM_F
REF0/(PCI_STOP#)
CPU1:3
PCI_F/MODE
XTAL
PLL Ref Freq
PLL 1
X2
X1
REF1/FS2
Stop
Clock
Control
Stop
Clock
Control
PCI2
PCI3
PCI4
48MHz/FS0
24MHz/FS1
PLL2
2,3
OSC
CLK_STOP#
PCI5
I
2
C
SDATA
Logic
SCLK
I/O Pin
Control
SDRAM0:11
SDRAMIN
12
VDDQ3
PCI1/FS3
Stop
Clock
Control
CPU_F
2
SDRAM_F
VDDQ3
REF0/(PCI_STOP#)*
GND
X1
X2
VDDQ3
PCI_F/MODE*
PCI1/FS3*
GND
PCI2
PCI3
PCI4
PCI5
VDDQ3
SDRAMIN
GND
SDRAM11
SDRAM10
VDDQ3
SDRAM9
SDRAM8
GND
SDATA
SCLK
W
1
56C
REF1/FS2*
VDDQ_CPU
CPU_F
CPU1
GND
CPU2
CPU3
CLK_STOP#*
GND
SDRAM_F
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
I
2
C
{
Notes:
1.
Internal pull-up resistors of 250 k
to 3.3V present on inputs indicated
with *.
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.
VDDQ3
VDDQ_CPU
VDDQ3
VDDQ3
W156C
PRELIMINARY
2
Pin Definitions
Pin Name
Pin No.
Pin
Type
Pin Description
CPU_F
46
O
Free-running CPU Clock: Output voltage swing is controlled by the voltage applied to
VDDQ_CPU. See Tables 2 and 6 for detailed frequency information.
CPU1:3
45,43,42
O
CPU Clock Output 1 through 3: These CPU clock outputs are controlled by the
CLK_STOP# control pin. Output voltage swing is controlled by voltage applied to
VDDQ_CPU.
PCI2:5
10, 11, 12, 13
O
PCI Clock Outputs 2 through 5: These four PCI clock outputs are controlled by the
PCI_STOP# control pin. Output voltage swing is controlled by voltage applied to
VDDQ3.
PCI1/FS3
8
I/O
Fixed PCI Clock Output: As an output, frequency is set by the FS0:3 inputs or through
serial input interface, see Tables 2 and 6. This output is affected by the PCI_STOP#
input. When an input, latches data selecting the frequency of the CPU and PCI outputs.
PCI_F/MODE
7
I/O
Fixed PCI Clock Output: As an output, frequency is set by the FS0:3 inputs or through
serial input interface, see Tables 2 and 6. This output is not affected by the PCI_STOP#
input. When an input, sets function of pin 2.
CLK_STOP#
41
I
CLK_STOP# Input: When brought LOW, affected clock outputs are stopped LOW after
completing a full clock cycle (23 CPU clock latency). When brought HIGH, affected
clock outputs start, beginning with a full clock cycle (23 CPU clock latency).
48MHz/FS0
26
I/O
48-MHz Output: 48 MHz is provided in normal operation. In standard systems, this
output can be used as the reference for the Universal Serial Bus. Upon power-up FS0
input will be latched, which will set clock frequencies as described in Table 2.
24MHz/FS1
25
I/O
24-MHz Output: 24 MHz is provided in normal operation. In standard systems, this
output can be used as the clock input for a Super I/O chip. Upon power-up FS1 input
will be latched, which will set clock frequencies as described in Table 2.
REF1/FS2
48
I/O
I/O Dual-Function REF0 and FS2 Pin: Upon power-up, FS2 input will be latched, which
will set clock frequencies as described in Table 2. When an output, this pin provides a
fixed clock signal equal in frequency to the reference signal provided at the X1/X2 pins.
REF0/
(PCI_STOP#)
2
I/O
Fixed 14.318-MHz Output 0 or PCI_STOP# Pin: Function determined by MODE pin.
The PCI_STOP# input enables the PCI 1:5 outputs when HIGH and causes them to
remain 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 signal provided at the
X1/X2 pins.
SDRAMIN
15
I
Buffered Input Pin: The signal provided to this input pin is buffered to 13 outputs
(SDRAM0:11, SDRAM_F).
SDRAM0:11
38, 37, 35, 34,
32, 31, 29, 28,
21, 20, 18, 17
O
Buffered Outputs: These twelve dedicated outputs provide copies of the signal provid-
ed at the SDRAMIN input. The swing is set by VDDQ3, and they are deactivated when
CLK_STOP# input is set LOW.
SDRAM_F
39
O
Free-running Buffered Output: This dedicated output provides a copy of the
SDRAMIN input which is not affected by the CLK_STOP# input.
SCLK
24
I
Clock pin for I
2
C circuitry.
SDATA
23
I/O
Data pin for I
2
C circuitry.
X1
4
I
Crystal Connection or External Reference Frequency Input: This pin has dual func-
tions. 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, this pin must be left unconnected.
VDDQ3
1, 6, 14, 19,
27, 30, 36
P
Power Connection: Power supply for core logic, PLL circuitry, SDRAM outputs, PCI
outputs, reference outputs, 48-MHz output, and 24-MHz output. Connect to 3.3V supply
VDDQ_CPU
47
P
Power Connection: Power supply for CPU_F and CPU1:3 output buffers. Connect to
3.3V.
GND
3, 9, 16, 22,
33, 40, 44
G
Ground Connections: Connect all ground pins to the common system ground plane.
W156C
PRELIMINARY
3
Overview
The W156C was developed as a single-chip device to meet the
clocking needs of VIA's MVP3 core logic chip set. In addition
to the typical outputs for CPU, Super IO, and PCI, the W156C
also provides 13 SDRAM clock outputs.
Cypress's proprietary spread spectrum frequency synthesis
technique is a feature of the CPU and PCI outputs. When en-
abled, this feature reduces the peak EMI measurements of not
only the output signals and their harmonics, but also of any
other clock signals that are properly synchronized to them.
Functional Description
I/O Pin Operation
Pins 7, 8, 25, 26, and 48 are dual-purpose l/O pins. Upon
power-up these pins act as logic inputs, allowing the determi-
nation 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 com-
bining clock outputs with input select pins.
An external 10-k
"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 and
Figure 2 show two suggested methods for strapping resistor
connections.
Upon W156C power-up, the first 2 ms of operation is used for
input logic selection. During this period, the five I/O pins (7, 8,
25, 26, 48) are three-stated, allowing the output strapping re-
sistor on the l/O pins to pull the pins and their associated ca-
pacitive clock load to either a logic HIGH or LOW state. At the
end of the 2-ms period, the established logic "0" or "1" condi-
tion of the l/O pin is latched. Next the output buffer is enabled,
converting the l/O pins into operating clock outputs. 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 signifi-
cant effect on clock output signal integrity. The drive imped-
ance of clock outputs is <40
(nominal), which is minimally
affected by the 10-k
strap to ground or V
DD
. As with the se-
ries 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 kept less than two inches in length to
minimize system noise coupling during input logic sampling.
When the clock outputs are enabled following the 2-ms input
period, the corresponding specified output frequency is deliv-
ered on the pin, 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
Q
D
W156C
V
DD
Clock Load
10 k
Output
Buffer
(L o a d O p tio n 1 )
10 k
(L o a d O p tio n 0 )
Output
Low
O utput S trapping R esistor
S e ries Te rm in ation R e sistor
Figure 1. Input Logic Selection Through Resistor Load Option
Power-on
Reset
Timer
Output Three-state
Data
Latch
Hold
Q
D
W156C
V
DD
Clock Load
R
10 k
Output
Buffer
Output
Low
Output Strapping Resistor
Series Termination Resistor
Jumper Options
Resistor Value R
Figure 2. Input Logic Selection Through Jumper Option
W156C
PRELIMINARY
4
Spread Spectrum Frequency Timing Generator
The device generates a clock that is frequency modulated in
order to increase the bandwidth that it occupies. By increasing
the bandwidth of the fundamental and its harmonics, the am-
plitudes of the radiated electromagnetic emissions are re-
duced. This effect is depicted in Figure 3.
As shown in Figure 3, a harmonic of a modulated clock has a
much lower amplitude than that of an unmodulated signal. 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 P is the percentage of deviation and F 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 Generation for the Reduction of Radiated Emissions" by
Bush, Fessler, and Hardin produces the maximum reduction
in the amplitude of radiated electromagnetic emissions. The
deviation selected for this chip is specified in Table 7. Figure 4
details the Cypress spreading pattern. Cypress does offer op-
tions 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 se-
lecting the appropriate values for bits 10 in data byte 0 of the
I
2
C data stream. Refer to Table 7 for more details.
Figure 3. Clock Harmonic with and without SSCG Modulation Frequency Domain Representation
SS FT G
Ty p ic al C loc k
Fre q ue n cy Sp an (M H z)
-S S%
+ S S%
A
m
pl
i
t
ude
(
d
B
)
5dB/div
MAX (+0.5%)
MIN (0.5%)
10
%
20
%
30
%
40
%
50
%
60
%
70
%
80
%
90
%
10
0%
10
%
20
%
30
%
40
%
50
%
60
%
70
%
80
%
90
%
10
0%
FREQ
UENCY
Figure 4. Typical Modulation Profile
W156C
PRELIMINARY
5
Serial Data Interface
The W156C features a two-pin, serial data interface that can
be used to configure internal register settings that control par-
ticular device functions. Upon power-up, the W156C 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
chipset. Clock device register changes are normally made
upon system initialization, if any are required. The interface
can also be used during system operation for power manage-
ment functions. Table 3 summarizes the control functions of
the serial data interface.
Operation
Data is written to the W156C in eleven bytes of eight bits each.
Bytes are written in the order shown in Table 4.
Table 3. Serial Data Interface Control Functions Summary
Control Function
Description
Common Application
Clock Output Disable
Any individual clock output(s) can be disabled.
Disabled outputs are actively held LOW.
Unused outputs are disabled to reduce EMI
and system power. Examples are clock
outputs to unused PCI slots.
CPU Clock Frequency
Selection
Provides CPU/PCI frequency selections through
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.
Spread Spectrum
Enabling
Enables or disables spread spectrum clocking.
For EMI reduction.
Output Three-state
Puts clock output into a high-impedance state.
Production PCB testing.
(Reserved)
Reserved function for future device 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 W156C to accept the bits in Data Bytes 06 for internal
register configuration. Since other devices may exist on the same com-
mon serial data bus, it is necessary to have a specific slave address for
each potential receiver. The slave receiver address for the W156C is
11010010. Register setting will not be made if the Slave Address is not
correct (or is for an alternate slave receiver).
2
Command Code
Don't Care
Unused by the W156C, therefore bit values are ignored ("don't care").
This byte must be included in the data write sequence to maintain
proper byte allocation. The Command Code Byte is part of the standard
serial communication protocol and may be used when writing to anoth-
er addressed slave receiver on the serial data bus.
3
Byte Count
Don't Care
Unused by the W156C, therefore bit values are ignored ("don't care").
This byte must be included in the data write sequence to maintain
proper byte allocation. The Byte Count Byte is part of the standard
serial communication protocol and may be used when writing to anoth-
er addressed slave receiver on the serial data bus.
4
Data Byte 0
Refer to Table 5
The data bits in Data Bytes 07 set internal W156C registers that con-
trol device operation. The data bits are only accepted when the Address
Byte bit sequence is 11010010, as noted above. For description of bit
control functions, refer to Table 5, Data Byte Serial Configuration Map.
5
Data Byte 1
6
Data Byte 2
7
Data Byte 3
8
Data Byte 4
9
Data Byte 5
10
Data Byte 6
11
Data Byte 7