Power management, Figure 65. apd unit – ST & T UPSD3212C User Manual
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POWER MANAGEMENT
All PSD MODULE offers configurable power sav-
ing options. These options may be used individu-
ally or in combinations, as follows:
–
The primary and secondary Flash memory,
and SRAM blocks are built with power
management technology. In addition to using
special silicon design methodology, power
management technology puts the memories
into Standby Mode when address/data inputs
are not changing (zero DC current). As soon
as a transition occurs on an input, the affected
memory “wakes up,” changes and latches its
outputs, then goes back to standby. The
designer does
not
have to do anything special
to achieve Memory Standby Mode when no
inputs are changing—it happens
automatically.
The PLD sections can also achieve Standby
Mode when its inputs are not changing, as
described in the sections on the Power
Management Mode Registers (PMMR).
–
As with the Power Management Mode, the
Automatic Power Down (APD) block allows
the PSD MODULE to reduce to standby
current automatically. The APD Unit can also
block MCU address/data signals from
reaching the memories and PLDs. The APD
Unit is described in more detail in
Built in logic monitors the Address Strobe of
the MCU for activity. If there is no activity for a
certain time period (MCU is asleep), the APD
Unit initiates Power-down Mode (if enabled).
Once in Power-down Mode, all address/data
signals are blocked from reaching memory
and PLDs, and the memories are deselected
internally. This allows the memory and PLDs
to remain in Standby Mode even if the
address/data signals are changing state
externally (noise, other devices on the MCU
bus, etc.). Keep in mind that any unblocked
PLD input signals that are changing states
keeps the PLD out of Standby Mode, but not
the memories.
–
PSD Chip Select Input (CSI, PD2) can be
used to disable the internal memories, placing
them in Standby Mode even if inputs are
changing. This feature does not block any
internal signals or disable the PLDs. This is a
good alternative to using the APD Unit. There
is a slight penalty in memory access time
when PSD Chip Select Input (CSI, PD2)
makes its initial transition from deselected to
selected.
–
The PMMRs can be written by the MCU at run-
time to manage power. The PSD MODULE
supports “blocking bits” in these registers that
are set to block designated signals from
reaching both PLDs. Current consumption of
the PLDs is directly related to the composite
frequency of the changes on their inputs (see
Figure
).
Significant power savings can be achieved by
blocking signals that are not used in DPLD or
CPLD logic equations.
Figure 65. APD Unit
APD EN
PMMR0 BIT 1=1
ALE
RESET
CSI
CLKIN
TRANSITION
DETECTION
EDGE
DETECT
APD
COUNTER
POWER DOWN
(PDN)
DISABLE BUS
INTERFACE
CSIOP SELECT
FLASH SELECT
SRAM SELECT
PD
CLR
PD
DISABLE
FLASH/SRAM
PLD
SELECT
AI06608