Herbie Murray
The LPC1768 microcontroller is a low-power, ARM Cortex-M3-based device featuring a wide range of peripherals, including UART. While it is possible to configure the RTC to generate an interrupt to wake up the MCU from Deep Sleep mode, it is unclear if UART can be used to wake up the LPC1768 from deep sleep or power-down modes. Some sources suggest that UART cannot be used for this purpose, while others provide workarounds, such as connecting the UART RTS pin to a PORT pin and enabling the interrupt for that pin. The LPC1549, another microcontroller, does support wake-up triggers received in UART, but it is unclear if the same methods can be applied to the LPC1768.
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What You'll Learn
LPC1768's Deep Power-Down mode
The LPC1768's Deep Power-Down mode is a power-saving feature that can be used to minimize current consumption in a board. In this mode, power is shut off to the entire chip, except for a few essential components like the Real-Time Clock (RTC), the RESET pin, the Wake-Up Interrupt Controller (WIC), and the RTC backup registers. This mode is particularly useful when the board needs to conserve as much power as possible.
To enter the Deep Power-Down mode, the RTC block must be configured to generate an interrupt after a predefined time, which will wake up the Microcontroller Unit (MCU) as expected. However, it has been observed that after the RTC interrupt, the MCU goes into a reset state, starting its execution from the beginning as if the reset button were pressed. This behaviour is unexpected and requires further investigation.
One possible solution to this issue is to store important data in the GPREG [0-4] register before entering Deep Power-Down mode. These registers can retain information even when the main power supply is off, ensuring that critical data is not lost during the reset process. Additionally, users can optimize power conservation by turning off or retaining power to the 32 kHz oscillator.
It is worth noting that the LPC1768 can wake up from Deep Power-Down mode via the RESET pin or an alarm match event of the RTC. This provides flexibility in managing power states and system interrupts. However, it is recommended to refer to the LPC1768 user manual and datasheet for detailed information and guidelines on utilizing the Deep Power-Down mode effectively.
In summary, the LPC1768's Deep Power-Down mode is a valuable feature for minimizing current consumption, but it requires careful configuration and an understanding of the system's behaviour to ensure optimal performance and data retention.
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LPC1768's low power mode
The LPC1768 microcontroller has several power-saving modes, including Sleep mode, Deep Sleep mode, Power-Down mode, and Deep Power-Down mode. In Sleep mode, the microcontroller can be woken up by an external interrupt, such as a UART interrupt. However, it is important to note that the Sleep mode does not turn off the watch dog, and there may be issues with the UART generating random data instead of the original data upon waking up from Sleep mode.
Deep Sleep mode offers further power savings by powering down peripherals, and can be used with the PHY turned off for even lower power consumption. Deep Sleep mode can be exited and the microcontroller can be woken up by an external interrupt.
Power-Down mode provides even greater power savings, and the microcontroller can be correctly woken up by configuring the RTC to generate an interrupt after a predefined time.
Deep Power-Down mode consumes the least power by shutting off power to the entire chip, except for the Real-Time Clock, the RESET pin, the WIC, and the RTC backup registers. However, this mode also causes a reset, and the microcontroller starts execution from the beginning as if the reset button was pressed. To optimize power conservation in Deep Power-Down mode, users can turn off or retain power to the 32 kHz oscillator, and they can use external circuitry to turn off power to the on-chip regulator via the VDD(REG)(3V3) pins. Wake-up from Deep Power-Down mode will occur when an external reset signal is applied or when the RTC interrupt is enabled and an RTC interrupt is generated.
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Configuring a pin as a wakeup source
Configuring a pin as a wake-up source is a straightforward process. The LPC1768 microcontroller offers a range of power-saving modes, including Deep Sleep and Deep Power-Down modes. In the Deep Power-Down mode, power is cut off from the entire chip, except for essential components like the Real-Time Clock, the RESET pin, the WIC, and the RTC backup registers.
To configure a pin as a wake-up source, you can follow these steps:
Step 1: Identify the Pin Functionality
Refer to the Pin Configuration Section in the datasheet of the LPC1768. Each pin has multiple functions, and you need to identify which pin you want to configure as the wake-up source. For example, pin number 37 (P0.0) can be configured as a GPIO – General Purpose Digital Input / Output Pin.
Step 2: Understand the Pin Connect Block
The Pin Connect Block is responsible for configuring the internal multiplexers to connect the pin to the on-chip peripheral, including GPIO. The Pin Connect Block allows you to select the function of each pin according to your requirements.
Step 3: Configure the Pin as Input or Output
Determine whether you want the pin to be an input or output. If set as an input, the MCU can read data from an external component in terms of voltage. If set as an output, the MCU will control the voltage on the pin, thus controlling the external component.
Step 4: Set the Pin as a Wake-Up Source
You can now set the selected pin as the wake-up source. This can be done by configuring the pin interrupt settings. For example, setting PIO1.0 as a pin interrupt and connecting it to GND can be used to wake up the MCU from deep sleep mode.
Step 5: Test the Configuration
After configuring the pin as the wake-up source, test the setup by putting the MCU into deep sleep mode. When the selected wake-up condition is met, the MCU should wake up, and you should see the expected behaviour, such as an LED lighting up or a message displayed on the UART.
By following these steps, you can effectively configure a pin as a wake-up source for the LPC1768 microcontroller, allowing you to customize the power management and functionality of your system.
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LPC1768's Deep Sleep mode
The LPC1768 microcontroller can be put into Deep Sleep or Power-Down modes, and it can wake up from these modes without any issues. However, when it comes to the Deep Power-Down mode, which consumes much less power, the LPC1768 exhibits a peculiar behaviour. After waking up from Deep Power-Down mode, the MCU goes into a reset state, starting its execution from the beginning as if the reset button were pressed.
To optimise power conservation, users can turn off or retain power to the 32 kHz oscillator in Deep Power-Down mode. Additionally, external circuitry can be used to turn off power to the on-chip regulator through the VDD(REG)(3V3) pins. It is important to restore power to the on-chip regulator before attempting to restart device operation.
The LPC1768 can be woken up from Deep Power-Down mode by applying an external reset signal or enabling the RTC (Real-Time Clock) interrupt. When the RTC interrupt is enabled and an RTC interrupt is generated, the LPC1768 will wake up. During Deep Power-Down mode, power is shut off to the entire chip, except for the RTC, the RESET pin, the WIC (Wake-up Interrupt Controller), and the RTC backup registers.
To achieve a successful Deep Power-Down recovery, it is recommended to store important data in the GPREG [0-4] register before entering this mode. The values in these registers are not affected by chip reset, ensuring data retention. Additionally, users should refer to the updated documentation for more information about the WIC, as the behaviour of the LPC1768 upon wake-up may be influenced by how it processes the next line of code.
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LPC1768's Power-Down mode
The LPC1768 microcontroller has various power-down modes, including Deep Sleep and Deep Power-Down modes. The Deep Power-Down mode is the most power-efficient option, as it shuts off power to the entire chip, except for the Real-Time Clock (RTC), the RESET pin, the WIC, and the RTC backup registers. The RTC can be used to generate an interrupt after a predefined time to wake up the MCU, but this can cause the MCU to reset and start execution from the beginning.
To optimise power conservation, users can choose to turn off or retain power to the 32 kHz oscillator. Additionally, external circuitry can be used to turn off power to the on-chip regulator via the VDD(REG)(3V3) pins after entering Deep Power-Down mode. However, power to the on-chip regulator must be restored before the device can be restarted.
Wake-up from Deep Power-Down mode can be achieved through an external reset signal or by enabling and generating an RTC interrupt. It is important to note that the wake-up behaviour may vary depending on the specific use case and configuration of the LPC1768.
The LPC1768 also supports Wake-On-Lan (WOL), which allows the device to be powered up remotely. This can be useful when managing multiple LPC1768s or for specific functions that require intermittent power. Additionally, the LPC1768 user manual provides instructions for waking up the device using the RTC alarm function from deep-sleep or power-down mode.
In summary, the LPC1768's Power-Down mode offers flexible options for power conservation, including Deep Sleep and Deep Power-Down modes. The Deep Power-Down mode is the most power-efficient option but may require additional steps for wake-up and data retention. Users can optimise power conservation through various configurations and utilise features like WOL and RTC alarm functions for customised power management.
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Frequently asked questions
No, UART cannot be used to wake up the LPC1768 from deep sleep or power-down modes.
To wake up the LPC1768 from deep sleep, you can configure the RTC to generate an interrupt after a predefined time.
The LPC1768 can also wake up from Deep Power-Down mode, Sleep mode, and Power-Down mode.
