Undershoot/Overshoot Requirements; Bsel[1:0] Implementation For Pga370 Designs; Bsel[1:0] Circuit Implementation For Pga370 Designs - Intel 810A3 Design Manual

2.2.2.5 Additional Considerations
•
Distribute Vtt with a wide trace. A 0.050" minimum trace is recommended to minimize DC
losses. Route the V
capacitors.
•
The V
condition.
•
Place resistor divider pairs for V
delivered to the processor.
2.2.3

Undershoot/Overshoot Requirements

Undershoot and overshoot specifications become more critical as the process technology for
microprocessors shrinks due to thinner gate oxide. Violating these undershoot and overshoot limits
will degrade the life expectancy of the processor.
2.2.4

BSEL[1:0] Implementation for PGA370 Designs

While the BSEL0 signal is still connected to the PGA370 socket, the Intel
does not utilize it. Only the Intel
®
Intel Pentium
However, the Intel
A new clock synthesizer, the CK810, has been designed to support selections of 66 MHz and
100 MHz. The REF input pin has been redefined to be a frequency selection strap (BSEL1) during
power-on and then becomes a 14 MHz reference clock output. This maintains pin compatibility
with the CK810 clock synthesizer.
Flexible PGA370 designs. Note that BSEL[1:0] are now pulled up using 1 KΩ resistors.
Figure 2-3
Figure 2-3. BSEL[1:0] Circuit Implementation for PGA370 Designs
®
Intel 810A3 Chipset Design Guide
trace to all components on the host bus. Be sure to include decoupling
TT
voltage should be 1.5V ±3% for static conditions, and 1.5V ±9% for transient
TT

®
III processors are 3.3V tolerant for these signals, as are the CK810 and GMCH.

Celeron processor requires 2.5V logic levels on the BSEL signals.
shows the GMCH and processor straps for selecting the system bus frequency:
3.3V 3.3V
1 ΚΩ
1 ΚΩ
B S E L 0
10 KΩ
L M D 2 9
PGA370 Processor Design Guidelines
generation at the GMCH component. V
REF
Celeron processor (PPGA) utilizes the BSEL0 signal. The
Figure 2-3 details the new BSEL[1:0] circuit design for
Processor
B S E L 1
10 KΩ
R E F
S E L 0
10 KΩ
L M D 1 3
G M C H
is also
REF
® ®
Pentium III processor
3.3V
8.2 KΩ
1 4 M H z
R E F C L K
CK810 S E L 1
2-9