Functional Description

I/O Pin Operation

Pin 27 is a dual-purpose l/O pin. Upon power-up this pin acts as a logic input, allowing the determination of assigned device functions. A short time after power-up, the logic state of the pin is latched and the pin becomes a clock output. This feature reduces device pin count by combining clock outputs with input select pins.

特性 Features

? Maximized EMI suppression using Cypress’s Spread Spectrum Technology

? Reduces measured EMI by as much as 10 dB

? I2C programmable to 133 MHz

? Two skew-controlled copies of CPU output

? SEL100/66# selects CPU frequency (100 or 66.8 MHz)

? Seven copies of PCI output (synchronous w/CPU output)

? One copy of 14.31818-MHz IOAPIC output

? One copy of 48-MHz USB output

? Selectable 24-/48-MHz clock is determined by resistor straps on power-up

? One high-drive output buffer that produces a copy of the 14.318-MHz reference

? Isolated core VDD pin for noise reduction