PLL202-03 PhaseLink (PLL), PLL202-03 Datasheet - Page 9

• Manufacturer Part Number: PLL202-03
• Description: Ali, Via, Sis, Intel 440BX Chipset FTGS , Freq. Progr., SST
• Manufacturer: PhaseLink (PLL)

PROGRAMMING OF CPU FREQUENCY
To simplify traditional loop counter setting, the PLL202-03 device incorporates SMART-BYTE ™
technology with a single byte programming via I2C to better optimize clock jitter and spread spectrum
performance. Detail of PLL202-03's dual mode frequency programming method is described below:
1. ROM-table Frequency Programming:
2. Micro-step Linear Frequency Programming:
FREQUENCY PROGRAMMING EXAMPLE:
1. Procedures to program target CPU frequency to 139.0 Mhz in Group A timing:
A. Locate the closest CPU frequency from Frequency-ROM table: 133.6
B.
C. Solve M (Linear Magnitude factor) in integer:
D. Program I2C register:
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The pre-defined 32 frequencies found in Frequency table can be accessed either through 5 external
jumpers or by setting internal I2C register in BYTE0.
CPU Frequency can be programmed via I2C in fine and linear positive or negative stepping around
selected CPU frequency in Frequency table. The highest step is either +127 or -127. Other bus
frequencies will be changed proportionally with the rate that CPU frequency change. The formula is
as follow:
= 0.22 for Group A
F
F
F
CPU
SDRAM
PCI
FS3 FS2 FS1 FS0 CTR FS4
Sign M6
Motherboard Clock Generator for SIS540/630 with 133MHz FSB
7
7
0 1 1 1 1 1 0 0
0 0 0 1 1 0 0 1
M = (F
6
6
= 133.6 + (0.22) * 25 = 139.1 ( % of frequency increased = 4.1 % )
= 133.6 * (1+4.1%)
= 33.4 * (1+4.1%)
= (139 – 133.6) / 0.22
= 25
M5
5
5
Where:
CPU
M4
4
4
- F
F
M3
CPU
3
3
CPU
-
M2
1. M is magnitude factor defined in I2C Byte 7.bit(0:6)
2.
3.
2
2
ROMTABLE
=
or
F
M1
1
1
CPU.ROM-Table
(sign bit) of M is defined in I2C Byte7.bit 7
is a constant but related to CPU's seven Timing groups definition
= 0.22 (for Group A, B) or
M0
= 0.11 (for Group E, F) or
0
0
= 139.1
= 34.7
) /
Setting of M = +25 in I2C.BYTE7
Setting of I2C.BYTE0
(=0.22, 0.15, 0.11 or 0.09)
= 0.15 (for Group C,D)
= 0.09 (for Group G)
*
M
PLL202-03
Rev 02/15/00 Page 9