CY28339
CPU_STOP# Deassertion
The deassertion of the CPU_STOP# signal will cause all
CPUT/C outputs that were stopped to resume normal
operation in a synchronous manner (meaning that no short or
stretched clock pulses will be produces when the clock
resumes). The maximum latency from the deassertion to
active outputs is no more than two CPUC clock cycles.
CPU_STP#
CPUT
CPUC
CPUT
CPUC
Figure 6. CPU_STOP# De-assertion Waveform
PCI_STOP# Assertion
Three-state Control of CPU Clocks Clarification
The PCI_STOP# signal is an active LOW input used for
synchronous stopping and starting the PCI outputs while the
rest of the clock generator continues to function. The set-up
time for capturing PCI_STOP# going LOW is 10 ns (tsetup) (see
Figure 2.) The PCIF clocks will not be affected by this pin if
their control bits in the SMBus register are set to allow them to
be free running.
During CPU_STOP# and PD# modes, CPU clock outputs may
be set to driven or undriven (tri-state) by setting the corre-
sponding SMBus entry in Bit6 of Byte0 and Bit6 of Byte1.
t setup
PCI_STP#
PCIF 33M
PCI 33M
Figure 7. PCI_STOP# Assertion Waveform
PCI_STOP# Deassertion
Byte 0,Bit 3. These two inputs to the function are logically
AND’ed. If either the external pin or the internal SMBus
register bit is set LOW, the stoppable PCI clocks will be
stopped in a logic LOW state. Reading SMBus Byte 0,Bit 3 will
return a 0 value if either of these control bits are set LOW
(which indicates that the devices stoppable PCI clocks are not
running).
The deassertion of the PCI_STOP# signal will cause all
PCI(0:2, 4:8) and stoppable PCIF clocks to resume running in
a synchronous manner within two PCI clock periods after
PCI_STOP# transitions to a HIGH level.
The PCI STOP function is controlled by two inputs. One is the
device PCI_STOP# pin number 34 and the other is SMBus
Rev 1.0,November 25, 2006
Page 9 of 17
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