Intel 31244 PCI-X manual Reference Clock Generation, Load Capacitance 20 pF Shunt Capacitance 7 pF

5.4.4Reference 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:

•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.)

Place the crystal near the GD31244 and isolated from noisy circuits as much as possible.

Design Guide 35