Pentium Processor Compatible Clock Synthesizer/Driver - Cypress Semiconductor
Description
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CY2254A
Pentium® Processor Compatible Clock Synthesizer/Driver
Features
• 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
Functional Description
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.
Logic Block Diagram
REF0 (14.
318 MHz) REF1 ...
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