16
ICS950810
0472F—01/12/04
When PWRDWN# is sampled low by two consecutive rising edges of CPU clock, then all clock outputs except CPU clocks
must be held low on their next high to low transitions. When the I2C Bit 6 of Byte 0 is programmed to '0' CPU clocks must
be held with the CPU clock pin driven high with a value of 2 x Iref, and CPU# undriven. If Bit 6 of Byte 0 is '1' then both
CPU and CPU# are undriven. Note the example below shows CPU = 133 MHz and Bit 6 of Byte 0 = '0', this diagram and
description is applicable for all valid CPU frequencies 66, 100, 133, 200 MHz.
Due to the state if the internal logic, stopping and holding the REF clock outputs in the LOW state may require more than
one clock cycle to complete.
PD# - Assertion (transition from logic "1" to logic "0")
Power Down Assertion of Waveforms
0ns
PD #
CPUT 100MHz
CPUC 100MHz
3V66MHz
PCI 33MHz
USB 48MHz
REF 14.318MHz
25ns 50ns
Power Down De-Assertion Mode
The power-up latency needs to be less than 1.8mS. this is the time from the de-asseration of the powerdown of the ramping
of the power supply until the time that stable clocks are output from the clock chip. If the I
2
C Bit 6 of Byte 0 is programmed
to "1" then the stopped CPU outputs will be driven high within 3 nS of PD# de-asseration.
