CY8C28xxx PSoC Programmable System-on-Chip TRM, Document No. 001-52594 Rev. *G
105
Sleep and Watchdog
Figure 12-1. Sleep Sequence
12.4.2
Wakeup Sequence
When asleep, the only event that can wake the system up is
an interrupt. The Global Interrupt Enable of the CPU flag
register does not need to be set. Any unmasked interrupt
will wake the system up. It is optional for the CPU to actually
take the interrupt after the wakeup sequence.
The wakeup sequence is synchronized to the 32 kHz clock
for purposes of sequencing a startup delay, to allow the
Flash memory module enough time to power up before the
CPU asserts the first read access. Another reason for the
delay is to allow the IMO, bandgap, and LVD/POR circuits
time to settle before actually being used in the system. As
shown in
, the wake up sequence is as follows.
1. The wakeup interrupt occurs and is synchronized by the
negative edge of the 32 kHz clock.
2. At the following positive edge of the 32 kHz clock, the
system-wide PD signal is negated. The Flash memory
module, IMO, and bandgap any POR/LVD circuits are all
powered up to a normal operating state.
3. At the next positive edge of the 32 kHz clock, the values
of the bandgap are settled and sampled.
4. At the following negative edge of the 32 kHz clock (after
about 15
s, nominal). The values of the POR/LVD sig-
nals have settled and are sampled. The BRQ signal is
negated by the sleep logic circuit. On the following CPU
clock, BRA is negated by the CPU and instruction exe-
cution resumes.
The wakeup times (interrupt to CPU operational) will range
from two to three 32 kHz cycles or 61 to 92
s (nominal).
IOW
SLEEP
BRQ
BRA
PD
On the falling edge of
CPUCLK, PD is asserted.
The 24/48 MHz system clock
is halted; the Flash and
bandgap are powered down.
CPUCLK
CPU captures
BRQ on next
CPUCLK edge.
Firmware write to
the SLEEP bit
causes an
immediate BRQ.
CPU
responds
with a BRA.
Summary of Contents for CY8C28 series
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