User`s manual
16 ASUS P5A-B User’s Manual
III. INSTALLATION
Jumpers
III. INSTALLATION
3. CPU External (BUS) Frequency Selection (FS0, FS1, FS2, FS3)
These jumpers tell the clock generator what frequency to send to the CPU. These
allow the selection of the CPU’s External frequency (or BUS Clock). The BUS Clock
times the BUS Ratio equals the CPU's Internal frequency (the advertised CPU speed).
4. CPU to BUS Frequency Ratio (BF0, BF1, BF2)
These jumpers set the frequency ratio between the Internal frequency of the CPU
and the External frequency (called the BUS Clock) within the CPU. These must be
set together with the above jumpers CPU External (BUS) Frequency Selection.
CPU External Clock (BUS) Frequency Selection
CPU : BUS Frequency Ratio
3.0x(3/1)
3.0x(3/1)
3.0x(3/1)
—
2.5x(5/2)
2.5x(5/2)
2.5x(5/2)
1.0x(1/1)
2.0x(2/1)
2.0x(2/1)
2.0x(2/1)
2.0x(2/1)
3.5x(7/2)
1.5x(3/2)
3.5x(7/2)
3.0x(3/1)
CPU A
CPU B
CPU C
CPU D
4.0x(4/1)
—
—
—
4.5x(9/2)
—
—
—
Match the “Ratio” column of the table on
the opposite page to these CPU types:
105MHz
70MHz
35MHz
1
2
3
110MHz
77.6MHz
38.8MHz
115MHz
77.6MHz
38.3MHz
120MHz
80MHz
40MHz
1
2
3
BF0
BF1
BF2
BF0
BF1
BF2
BF0
BF1
BF2
BF0
BF1
BF2
BF0
BF1
BF2
BF0
BF1
BF2
CPU
AGP
PCI
→
→
→
P5A-B
→
→
→
→
R
60MHz
60MHz
30MHz
1
2
3
FS0
FS1
FS2
66.8MHz
66.8MHz
33.4MHz
75MHz
75MHz
37.5MHz
83.3MHz
66.6MHz
33.3MHz
95MHz
63.3MHz
31.6MHz
100MHz
66.6MHz
33.3MHz
FS0
FS1
FS2
FS0
FS1
FS2
FS0
FS1
FS2
FS0
FS1
FS2
CPU
AGP
PCI
→
→
→
FS3
FS3
FS3
FS3
FS3
5.0x(5/1)
—
—
—
BF0
BF1
BF2
WARNING! Frequencies above 100MHz exceed the specifications for the on-
board chipset and are not guaranteed to be stable. The table on the following
page is for general reference purposes only. Always refer to the instructions in-
cluded with your CPU when possible.
CPU A: AMD-K6-2, AMD-K6
CPU B: Intel Pentium P54C, AMD-K5
CPU C: Intel Pentium P55C, IBM/Cyrix 6x86MX, IBM/Cyrix M II
CPU D: IBM/Cyrix 6x86, IBM/Cyrix 6x86L