PLL205-01 Datasheet, PDF (8/12 Pages) List of Unclassifed Manufacturers – Motherboard Clock Generator for AMD - K7

PLL205-01
Motherboard Clock Generator for AMD - K7
PROGRAMMING OF CPU FREQUENCY
To simplify traditional loop counter setting, the PLL205-01 device incorporates SMART-BYTE ™
technology with a single byte programming via I2C to better optimize clock jitter and spread spectrum
performance. Detail of PLL205-01's dual mode frequency programming method is described below:
1. ROM-table Frequency Programming:
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.
2. Micro-step Linear Frequency Programming:
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:
F F CPU = CPU.ROM-Table ± α (=0.22)* M
Where:
1. M is magnitude factor defined in I2C Byte 7.bit(0:6)
2. ± (sign bit) of M is defined in I2C Byte7.bit 7
3. α is a constant
α = 0.22
FREQUENCY PROGRAMMING EXAMPLE:
1. Procedures to program target CPU frequency to 139.0 Mhz:
A. Locate the closest CPU frequency from Frequency-ROM table: 136.5
B. α = 0.22
C. Solve M (Linear Magnitude factor) in integer:
M = (FCPU - FCPU-ROMTABLE) / α
= (139 – 136.5) / 0.22
= 11
D. Program I2C register:
76543210
01101100
FS3 FS2 FS1 FS0 CTR FS4
76543210
00001011
Sign M6 M5 M4 M3 M2 M1 M0
Setting of I2C.BYTE0
Setting of M = +11 in I2C.BYTE7
FCPU = 136.5 + (0.22) * 11 = 138.92 ( % of frequency increased = 1.8 % )
FPCI = 34.1 * (1+1.8%) = 34.7
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Rev 03/07/00 Page 8