PSD813F1 STMICROELECTRONICS [STMicroelectronics], PSD813F1 Datasheet - Page 71

• Manufacturer Part Number: PSD813F1
• Description: Flash In-System Programmable ISP Peripherals For 8-bit MCUs
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

Preliminary
The
PSD813F1
Functional
Blocks
(cont.)
9.5 Power Management
The PSD813F1 offers configurable power saving options. These options may be used
individually or in combinations, as follows:
9.5.1 Automatic Power Down (APD) Unit and Power Down Mode
The APD Unit, shown in Figure 30, puts the PSD into Power Down Mode by monitoring
the activity of the address strobe (ALE/AS). If the APD unit is enabled, as soon as activity
on the address strobe stops, a four bit counter starts counting. If the address strobe
remains inactive for fifteen clock periods of the CLKIN signal, the Power Down (PDN) signal
becomes active, and the PSD will enter into Power Down Mode, discussed next.
All memory types in a PSD (Flash, EEPROM, and SRAM) are built with Zero-Power
technology. In addition to using special silicon design methodology, Zero-Power
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,
see PMMR registers below.
Like the Zero-Power feature, the Automatic Power Down (APD) logic allows the PSD to
reduce to standby current automatically. The APD will block MCU address/data signals
from reaching the memories and PLDs. This feature is available on all PSD813F1
devices. The APD unit is described in more detail in section 9.5.1.
Built in logic will monitor the address strobe of the MCU for activity. If there is no activity
for a certain time period (MCU is asleep), the APD logic initiates Power Down Mode
(if enabled). Once in Power Down Mode, all address/data signals are blocked from
reaching PSD memories and PLDs, and the memories are deselected internally. This
allows the memories and PLDs to remain in standby mode even if the address/data
lines 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.
The PSD Chip Select Input (CSI) on all families 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 logic, especially if your MCU has a chip select output. There is a slight
penalty in memory access time when the CSI signal makes its initial transition from
deselected to selected.
The PMMR registers can be written by the MCU at run-time to manage power.
PSD813F1 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 Figures
34 and 34a). Significant power savings can be achieved by blocking signals that are
not used in DPLD or CPLD logic equations.
The PSD813F1 has a Turbo Bit in the PMMR0 register. This bit can be set to disable
the Turbo Mode feature (default is Turbo Mode on). While Turbo Mode is disabled, the
PLDs can achieve standby current when no PLD inputs are changing (zero DC current).
Even when inputs do change, significant power can be saved at lower frequencies
(AC current), compared to when Turbo Mode is enabled. When the Turbo Mode is
enabled, there is a significant DC current component and the AC component is higher.
PSD813F1-A
67