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ICS94258

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PD# Timing Diagram

The power down selection is used to put the part into a very low power state without turning off the power to the part. PD# is

an asynchronous active low input. This signal needs to be synchronized internal to the device prior to powering down the clock

synthesizer.

Internal clocks are not running after the device is put in power down. When PD# is active low all clocks need to be driven to a

low value and held prior to turning off the VCOs and crystal. The power up latency needs to be less than 3 mS. The power down

latency should be as short as possible but conforming to the sequence requirements shown below. PCI_STOP# and

CPU_STOP# are considered to be don't cares during the power down operations. The REF and 48MHz clocks are expected to

be stopped in the LOW state as soon as possible. Due to the state of the internal logic, stopping and holding the REF clock

outputs in the LOW state may require more than one clock cycle to complete.

Notes:

1. All timing is referenced to the Internal CPUCLK (defined as inside the ICS94258 device).

2. As shown, the outputs Stop Low on the next falling edge after PD# goes low.

3. PD# is an asynchronous input and metastable conditions may exist. This signal is synchronized inside this part.

4. The shaded sections on the VCO and the Crystal signals indicate an active clock.

5. Diagrams shown with respect to 133MHz. Similar operation when CPU is 100MHz.

CPUCLK

PCICLK

VCO

Crystal

PD#