Intel Pentium 4

Platform Clock Routing Guidelines
R
46 Intel
®
Pentium
®
4 Processor / Intel
®
850 Chipset Family Platform Design Guide
4.2 BCLK[1:0] Frequency Select
4.2.1 100 MHz Operation – Intel
®
82850 Chipset
The BCLK[1:0] frequency should be set for 100 MHz operation for the 82850 chipset. This is
accomplished with a 470 Ω pull-down on the CK-00 SEL100/133 input. In addition, the platform
should be prevented from operating with a processor that requires a BCLK[1:0] frequency other
than 100 MHz. The correct frequency select circuitry is show in Figure 16.
Figure 16. BCLK[1:0] Frequency Select for 100 MHz System Bus Operation
470Ω
CK-00Processor
3.3V
SEL 100/133
PWRDWN#
BSEL0
1kΩ
1kΩ
3.3V
BCLK_Freq_Sel