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UG-1262
Rev. B | Page 26 of 312
Flexi Mode
In this mode, the Arm Cortex-M3 is disabled. The user selects the peripherals to be enabled, for example, SPI for DMA or I
2
C for DMA.
Hibernate Mode
On the digital die, the system is power gated. 8 kB of SRAM is always retained. Up to an additional 24 kB SRAM can be selected to be
retained. PMG0 PWRMOD, Bits[1:0] = 10.
On the analog die, the high speed oscillator and high speed clock source are powered down so that all blocks clocked by these clock
sources are clock gated. The 32 kHz oscillator and the analog die watchdog timer remains active. Optionally, the low power DACs, low
power reference, and low power amplifiers can remain active to keep an external sensor biased. ALLON PWRMOD, Bits[1:0] = 10.
POWER MANAGEMENT UNIT OPERATION
The debug tools can prevent the Arm Cortex-M3 from fully entering power saving modes by setting bits in the debug logic. Only a
power-on reset (POR) can reset the debug logic. Therefore, the device must be power cycled after using the serial wire debug with an
application code containing the wait for interrupt (WFI) instruction.
Active Mode, Mode 0
The system is fully active. Memories and all user enabled peripherals are clocked, and the Arm Cortex-M3 processor executes
instructions. The Arm Cortex-M3 processor manages its internal clocks and can be in a partial clock gated state. This clock gating affects
only the internal Arm Cortex-M3 processing core. Automatic clock gating is used on all blocks except the I
2
C, UART, and general-
purpose timers. These blocks are manually clock gated using the CLKG CTL5 register for the digital die and the CLKEN1 register for the
analog die.
The user code can use a WFI command to put the Arm Cortex-M3 processor into sleep mode. The processor is independent of the
power mode settings of the PMU.
Writing 1 to CLKG CTL5, Bits[5:0] or AFE CLKEN1, Bits[9:0] stops the corresponding clock to peripherals. For the digital die
peripherals, after the clock stops, if the user or software accesses any register in that peripheral, the clock is automatically enabled. In
addition, writing 0 to these bits in the CLKG CTL5 or AFE CLKEN1 registers enables the corresponding clock to the peripheral.
Chip power-up with the LDO regulator is on by default on both die. The buck regulator can be enabled to save power consumption by
writing 1 to the PMG0 CTL1, Bit 0. When enabled, the input to the on-chip 1.2 V LDO regulator is the buck converter output, which is
typically 1.6 V.
When the
wakes up from any of the low power modes, the device returns to Mode 0.
Flexi Mode, Mode 1 (Digital Die Only)
In Flexi mode, the system gates the clock to the Arm Cortex-M3 core after the Arm Cortex-M3 enters power-down by executing the WFI
instruction. The rest of the system remains active, and no instructions can be executed. However, DMA transfers can continue to occur
between peripherals and memories. The Arm Cortex-M3 processor, RCLK (clock to flash), is active, and the device wakes up using the
nested vectored interrupt controller (NVIC).
Hibernate Mode, Mode 2
To enter hibernate mode, the user must first configure the analog die for hibernate by setting ALLON PWRMOD, Bits[1:0] = 10, and
then, the user can place the digital die into hibernate mode. To minimize current consumption, configure unused digital GPIO pins as
tristate on both die.
On the digital die, in hibernate mode, the Arm Cortex-M3 and all digital peripherals are turned off. The SRAM can be programmed to
retain up to 32 kB. The user can select the following:
The amount of SRAM to retain. This amount is in addition to the 8 kB of SRAM always retained in the hibernate mode. This
selection is controlled using SRAMRET, Bits[1:0].
Control battery monitoring during hibernate mode. The regulated 1.2 V supply is always monitored to guarantee that data is never
corrupted by the supply going below the minimum retention voltage. If the regulated supply falls below 1 V, the chip resets before
any data is corrupted. Though the regulated supply is always monitored, there is an option to also monitor the AVDD_DD pin
(2.8 V to 3.6 V supply) in hibernate mode by clearing PMG0 PWRMOD, Bit 3 = 0.
On the analog die, in hibernate mode, the AFE high speed clock circuits are powered down, causing all blocks clocked by these circuits to
enter a low power, clock gated state. After setting ALLON PWRMOD, Bits[1:0] = 10, do not read back the value of the register because
this read can halt the entry of the analog die into hibernate mode.