SAM4CM Series [DATASHEET]
Atmel-11203C-ATARM-SAM4CM32-SAM4CM16-SAM4CM8-Datasheet_06-Oct-14
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5.5
Low-power Modes
The various low-power modes (Backup, Wait and Sleep modes) of the SAM4CM are described below. Note that
the Segmented LCD Controller can be used in all low-power modes.
Note:
The Wait For Event instruction (WFE) of the Cortex-M4 core can be used to enter any of the low-power modes,
however this may add complexity to the design of application state machines. This is due to the fact that the WFE
instruction is associated with an event flag of the Cortex core that cannot be managed by the software application. The
event flag can be set by interrupts, a debug event or an event signal from another processor. When an event occurs
just before WFE execution, the processor takes it into account and does not enter Low-power mode. Atmel has made
provision to avoid using the WFE instruction. The workarounds to ease application design, including the use of the
WFE instruction, are given in the following description of the low-power mode sequences.
5.5.1
Backup Mode
The purpose of Backup mode is to achieve the lowest possible power consumption in a system that executes
periodic wake-ups to perform tasks but which does not require fast start-up time. The total current consumption is
0.5 μA typical on VDDBU.
The Supply Controller, power-on reset, RTT, RTC, backup registers and the 32 kHz oscillator (RC or crystal
oscillator selected by software in the Supply Controller) are running. The regulator and the core supplies are off.
The power-on-reset on VDDBU can be deactivated by software.
Wake-up from Backup mode can be done through the Force Wake-up (FWUP) pin, WKUP0, WKUP1 to WKUP15
pins, the VDDIO Supply Monitor (SM) if VDDIO is supplied, or through an RTT or RTC wake-up event. Wake-up
pins multiplexed with anti-tampering functions are additional possible sources of a wake-up if an anti-tampering
event is detected. The TMP0 pad is supplied by the backup power supply (VDDBU). TMP1 is supplied by VDDIO.
The LCD Controller can be used in Backup mode. The purpose is to maintain the displayed message on the LCD
display after entering Backup mode. The current consumption on VDDIN to maintain the LCD is 10 μA typical.
In case the VDDIO power supply is maintained with VDDBU when entering Backup mode, it is up to the application
to configure all PIO lines in a stable and known state to avoid extra power consumption or possible current path
with the input/output lines of the external on-board devices.
5.5.1.1 Entering and Exiting Backup Mode
To enter Backup mode, follow the steps in the sequence below:
1.
Depending on the application, set the PIO lines in the correct mode and configuration (input pull-up or pull-
down, output low or high levels).
2.
Disable the Main Crystal Oscillator (enabled by SAM-BA boot if the device is booting from ROM).
3.
Configure PA30/PA31 (XIN/XOUT) into PIO mode depending on their use.
4.
Disable the JTAG lines using the SFR1 register in Matrix 0 (by default, internal pull-up or pull-down is
disabled on JTAG lines).
5.
Enable the RTT in 1 Hz mode.
6.
Disable Normal mode of the RTT (RTT will run in 1 Hz mode).
7.
Disable the POR backup if not needed. This increases power efficiency.
8.
Disable the Core brownout detector.
9.
Select one of the following methods to complete the sequence:
a.
To enter Backup mode using the VROFF bit:
Write a 1 to the VROFF bit of SUPC_CR.
b.
To enter Backup mode using the WFE instruction:
Write a 1 to the SLEEPDEEP bit of the Cortex-M4 processor.
Execute the WFE instruction of the processor.