LPC11U68 deep power down

A review of document

UM10732LPC11U6x/E6x User manual Rev. 1.3 — 19 May 2014

Wake Up sources

• Deep power-down WAKEUP pin PIO0_16
• RTC 1 kHz timer time-out and alarm

Conditions

• Enable the WAKEUP function in the GPREG4 register in the PMU(Power Management Unit).
• Enable the RTC oscillator in the RTC CTRL register.
• Enable RTC alarm signal to wake up the part from Deep power-down mode in the RTC CTRL register.
• Select RTC clock in the RTC CTRL register.
• Start RTC wake-up timer by writing a time-out value to the RTC WAKE register

Programming Deep power-down mode

The following steps must be performed to enter Deep power-down mode:

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1. Pull the WAKEUP pin externally HIGH.
2. Ensure that bit 3 in the PCON register (Table 77) is cleared.
3. Write 0x3 to the PD bits in the PCON register (see Table 77).
4. Store data to be retained in the general purpose registers (Section 5.4.2).
5. Write one to the SLEEPDEEP bit in the ARM Cortex-M0 SCR register.
6. Use the ARM WFI instruction.

Wake-up from Deep power-down mode

Pulling the WAKEUP pin LOW wakes up the part from Deep power-down, and the chip goes through the entire reset process

1. On the WAKEUP pin, transition from HIGH to LOW.

• The PMU will turn on the on-chip voltage regulator. When the core voltage reaches the power-on-reset (POR) trip point, a system reset will be triggered and the chip re-boots.
• All registers except the GPREG0 to GPREG4 and PCON will be in their reset state.

1. Once the chip has booted, read the deep power-down flag in the PCON register (Table 77) to verify that the reset was caused by a wake-up event from Deep power-down and was not a cold reset.
2. Clear the deep power-down flag in the PCON register (Table 77).
3. (Optional) Read the stored data in the general purpose registers (Section 5.4.2).
4. Set up the PMU for the next Deep power-down cycle.

• Remark: The RESET pin has no functionality in Deep power-down mode.

Programming Deep power-down mode using the RTC for wake-up

The following steps must be performed to enter Deep power-down mode when using the RTC for waking up:

1. Set up the RTC high-resolution timer. Write to the RTC VAL register. This starts the high-resolution timer if enabled. Another option is to use the 1 Hz alarm timer.
2. Ensure that bit 3 in the PCON register (Table 77) is cleared.
3. Store data to be retained in the general purpose registers (Section 5.4.2).
4. Use the ARM WFI instruction

Wake-up from Deep power-down mode using the RTC

The part goes through the entire reset process when the RTC times out:

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1. When the high-resolution timer count reaches 0, the following happens:

– The PMU will turn on the on-chip voltage regulator. When the core voltage reaches

the power-on-reset (POR) trip point, a system reset will be triggered and the chip boots.

– All registers except the GPREG0 to GPREG4 registers and PCON will be in their reset state.

1. Once the chip has booted, read the deep power-down flag in the PCON register

(Table 77) to verify that the reset was caused by a wake-up event from Deep power-down and was not a cold reset.

1. Clear the deep power-down flag in the PCON register (Table 77).
2. (Optional) Read the stored data in the general purpose registers (Section 5.4.2).
3. Set up the PMU for the next Deep power-down cycle.

RTC

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• RTC alarm and high-resolution/wake-up timer time-out each generate independent interrupt requests. Either time-out can wake up the part from any of the low power modes, including Deep power-down

RTC CTRL register

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• This register controls which clock the RTC uses (1.024 kHz or 1 Hz) and enables the two

RTC interrupts to wake up the part from Deep power-down.

• To wake up the part from Deep-sleep or Power-down modes, enable the RTC interrupts in the system control block

STARTLOGIC1 register.