Pentium Processor Compatible 28-Pin SOIC T/R

The CY2254A is a Clock Synthesizer/Driver that provides the multiple clocks required for a Pentium-based PC. The CY2254A has low-skew outputs (=250 ps between the CPU Clocks, = 250 ps between the PCI Clocks). In addition, the CY2254A CPU clock outputs have less than 200 ps cycle-to-cycle jitter. Finally, both the PCI and CPU clock outputs meet the 1 V/ns slew rate requirement of a Pentium processor-based system. The CY2254A accepts a 14.318 MHz reference signal as its input. The CY2254A has 2 PLLs, one of which generates the CPU and PCI clocks, and the other generates the I/O and Keyboard Controller or USB clocks. The CY2254A runs off either a 3.3V or 5V supply. The CY2254A is available in two options. The 1 option supports the Intel Triton PCIset and provides a 12 MHz keyboard clock on pin 25. The 2 option provides a 48 MHz USB clock on pin 25 and supports the Cyrix M1 processor.

• Multiple clock outputs to meet requirements of most Pentium® motherboards
  • Four pin-selectable CPU clocks @ 66.66 MHz, 60.0 MHz, and 50.0 MHz for support of Intel Triton™ PCIset based PC
  • 55.0 MHz pin-selectable CPU clock also available ( 2 option only)
  • Six PCI clocks at 1/2 CPU Clock frequency
  • One I/O clock @ 24 MHz
  • One Keyboard Controller clock @ 12 MHz ( 1 option) or one Universal Serial Bus clock @ 48 MHz ( 2 option)
  • Two Ref. clocks @ 14.318 MHz
  • Ref. 14.318 MHz Xtal oscillator input
• CPU clock jitter < 200 ps cycle-to-cycle
• Low skew outputs
  • = 250 ps between CPU clocks
  • = 250 ps between PCI clocks
  • = 500 ps between CPU and PCI clocks ( 2 option)
  • CPU clock leads PCI clock by +1 ns min. to +4 ns max. ( 1 option)
• Freq. stability = 0.01% (max.)
• Output duty cycle 45% min. to 55% max.
• Test mode support ( 1 option only)
• 3.3V or 5.0V operation
• Internal pull-up resistors on S0, S1, and OE inputs