19.4 Power Consumption Control

Many things in life are powered by microcontrollers, and a considerable number of devices, instruments, and products rely on batteries for power supply. Often, these devices, instruments, and products powered by batteries can be used for a long time. For example, if the MCU of the remote control we often use keeps running, the battery energy will be exhausted in a short period of time. Of course, in the system equipped with NuMicro M051 series microcontrollers, not only the microcontroller needs to consume power, but also other peripheral components. Therefore, we shut down the operation of the equipment at the appropriate time and put the operation mode of the NuMicro M051 series microcontroller into idle mode or power-off mode to save unnecessary energy and achieve the purpose of low power consumption.

Normally, the current of the NuMicro M051 series microcontroller is 4 mA to 7 mA when it is in normal operation; when it enters the power-down mode, its operating current is less than 1 micro ampere. Therefore, it is necessary to control the power consumption of low-power devices and put them in the power-down mode at the appropriate time. At the same time, the operating frequency of the MCU based on the ARM Cortex-M0 core can reach 50MHz, and the minimum operating frequency is 4MHz. When conditions permit, the MCU does not need to run at 50MHz.

When the MCU enters the idle mode, except for the CPU in the dormant state, all other hardware is in the active state. The data in the data memory and special function registers not involved in the program in the chip will keep the original value during the idle mode. But if the timer is running, the value in the counter register will increase. The MCU can be awakened by any interrupt or hardware reset in the idle mode. It should be noted that when the interrupt is used to wake up the MCU, the program will continue to run from the original stop point. When the hardware reset is used to wake up the MCU, the program will start from the beginning.

When the MCU enters power-down mode, the external crystal oscillator stops, the CPU, timer, and serial port all stop working, and only the external interrupt continues to work. The instruction that puts the MCU into sleep mode will be the last instruction executed by the MCU before sleep. After entering sleep mode, the data in the data memory and special function registers not involved in the program in the chip will maintain the original value. The MCU can be awakened by an external interrupt low level trigger, a falling edge trigger interrupt, or a hardware reset mode. It should be noted that when the MCU is awakened by an interrupt, the program continues to run from the original stop point. When the MCU is awakened by a hardware reset, the program will start from the beginning.