Intel III 450 MHz 80525PY450512 Data Sheet
Product codes
80525PY450512
22
Datasheet
Electrical Specifications
2.8.2
System Bus Frequency Select Signal (BSEL0)
The BSEL[1:0] signals (BSEL0 is also known as 100/66#) are used to select the system bus
frequency for the Pentium III processor(s).
frequency for the Pentium III processor(s).
defines the possible combinations of the signals
and the frequency associated with each combination. The frequency is determined by the
processor(s), and frequency synthesizer. All system bus agents must operate at the same core and
system bus frequency in a 2-way MP Pentium III processor configuration. In a 2-way MP system
design, the BSEL[1:0] signals must be connected to the BSEL[1:0] pins of both processors. The
Pentium III processor operates at either a 100 MHz or 133 MHz system bus frequency, but not
both. 66 MHz system bus operation is not supported.
processor(s), and frequency synthesizer. All system bus agents must operate at the same core and
system bus frequency in a 2-way MP Pentium III processor configuration. In a 2-way MP system
design, the BSEL[1:0] signals must be connected to the BSEL[1:0] pins of both processors. The
Pentium III processor operates at either a 100 MHz or 133 MHz system bus frequency, but not
both. 66 MHz system bus operation is not supported.
For systems that support only a 100 MHz system bus clock, resistors on the processor cartridge
will tie the BSEL1 signal to ground (as shown in
will tie the BSEL1 signal to ground (as shown in
). This signal can either be left as a no
connect or tied to ground as shown below. The BSEL0 should be pulled up to 3.3 V with a 220
Ω
resistor, and provided as a frequency driver to the clock driver/synthesizer.
On baseboards which support operation at either 100 or 133 MHz, the BSEL[1:0] signals should be
pulled up to 3.3 V with a 220
pulled up to 3.3 V with a 220
Ω
resistor (as shown in
and
) and BSEL1 is
provided as a frequency selection signal to the clock driver/synthesizer. The BSEL0 signal can also
be incorporated into system shutdown logic on the baseboard (thus forcing the system to shutdown
as long as the BSEL0 signal is low).
be incorporated into system shutdown logic on the baseboard (thus forcing the system to shutdown
as long as the BSEL0 signal is low).
shows this routing example with a 100 MHz
shows the same routing example with a 133 MHz Pentium III
processor.
Table 5. Frequency Select Truth Table for BSEL[1:0]
BSEL1
BSEL0
Frequency
0
0
66 MHz (unsupported)
0
1
100 MHz
1
0
Reserved
1
1
133 MHz
Figure 4. BSEL[1:0] Example for a 100 MHz System Design (100 MHz Processor Installed)
Processor
Core
GND
GND
BSEL1
0
Ω
0
Ω
1
ΚΩ
3.3
ΚΩ
100/66#
CK100
GND
3.3V
220
Ω
BSEL0
S
C
C
2
4
2
4
2
Intel
®
Pentium
®
III Processor