Description
The FS6251-01 is a CMOS clock generator IC designed for high-speed motherboard applications. Two different frequencies can be selected for the CPU and PCI clocks via two SEL pins. Glitch-free stop clock control of the CPU and PCI clocks is provided. A low current power down mode is available for mobile applications. Separate clock buffers provide for a 2.5V voltage range on the CPU_0:3 and APIC_0:1 clocks.

Features
• Generates clocks required for Intel Pentium® II based systems, including:
   ♦ Four enabled 2.5V 100MHz or 66MHz CPU sys tem bus clock outputs
   ♦ Seven enabled 3.3V PCI bus clocks and one free-running PCI clock
   ♦ Three 3.3V REF clocks at 14.318MHz
   ♦ Two 2.5V APIC clocks at 14.318MHz for APIC bus timing
   ♦ Two 3.3V 48MHz clocks for 4x Universal Serial Bus (USB) timing
• Non-linear spread spectrum modulation (-0.5% at 31.5kHz)
• Selectable 100MHz or 66MHz system bus clock
• Supports Intel Test Mode and tristate output control to facilitate board testing
• Synchronous clocks skew-matched to <175ps on CPU and APIC buffers and <250ps on PCI buffers
• Separate CPU-enable, PCI-enable and power-down inputs with glitch-free stop clock controls on all clocks for clock control and power management
• All inputs and 3.3V outputs are LVTTL-compatible