Intel 31244 PCI-X User Manual
35
5.4.4
Reference Clock Generation
A 37.5 MHz reference clock with a +/- 100 ppm accuracy is required for proper operation of the
GD31244. This is generated from an external oscillator connected directly to the XI input.
Optionally, a 37.5 MHz crystal may be connected between the XI and XO pins with a 20 pF
capacitor from XI to ground and another from XO to ground. The following are the crystal
characteristics:
GD31244. This is generated from an external oscillator connected directly to the XI input.
Optionally, a 37.5 MHz crystal may be connected between the XI and XO pins with a 20 pF
capacitor from XI to ground and another from XO to ground. The following are the crystal
characteristics:
•
Frequency: 37.5 MHz +/- 100 ppm
•
Mode: Fundamental
•
Type: Parallel resonant
•
ESR: 30 Ohms maximum
•
Load Capacitance: 20 pF
•
Shunt Capacitance: 7 pF
•
Drive Level: 500 mW maximum
•
Recommended Vendor/Part Number: Fox Electronics, Part number: 278-37.5-8 (This is an
HC-49SD surface mountable package.)
HC-49SD surface mountable package.)
Place the crystal near the GD31244 and isolated from noisy circuits as much as possible.