16

ICS94228

0447E—05/07/04

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 ICS94228 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.

CPUCLKT

CPUCLKC

PCICLK

VCO

Crystal

PD#

PCI_STOP# Timing Diagram

PCI_STOP# is an asynchronous input to the ICS94228. It is used to turn off the PCICLK clocks for low power operation.

PCI_STOP# is synchronized by the ICS94228 internally. The minimum that the PCICLK clocks are enabled

(PCI_STOP# high pulse) is at least 10 PCICLK clocks. PCICLK clocks are stopped in a low state and started with a

full high pulse width guaranteed. PCICLK clock on latency cycles are only one rising PCICLK clock off latency is one

PCICLK clock.

Notes:

1. All timing is referenced to the Internal CPUCLK (defined as inside the ICS94228 device.)

2. PCI_STOP# is an asynchronous input, and metastable conditions may exist. This signal is required to be synchronized

inside the ICS94228.

3. All other clocks continue to run undisturbed.

4. CPU_STOP# is shown in a high (true) state.

CPUCLK

(Internal)

PCICLK_F

(Internal)

PCICLK_F

(Free-running)

CPU_STOP#

PCICLK

PCI_STOP#