Research and design of ultra-low power consumption of MSP430G2553 microcontroller

Introduction
The MSP430 series of microcontrollers launched by     Texas Instruments (TI) can achieve extremely low processor power consumption, which is particularly suitable for battery-powered applications. This article takes the MSP430G2553 microcontroller as an example to discuss its design to achieve ultra-low power consumption in more detail.

1 Overview of MSP430G2553 Microcontroller
    The MSP430 series of microcontrollers has ultra-low power consumption characteristics, as well as powerful data processing and computing capabilities, high-performance analog technology, rich on-chip modules, and a convenient and efficient development and debugging environment. The MSP430G2553 microcontroller is a mixed-signal microcontroller with a 16-bit reduced instruction set (RISC) architecture and a 62.5 ns instruction cycle time. It can wake up from standby mode ultra-fast in less than 1μs and supports JTAG simulation debugging. Ultra-low power consumption: 1.8-3.6 V low power supply voltage; under 1 MHz frequency and 2.2 V voltage conditions, there are 230 μA/running mode, 0.5 μA/standby mode, 0.1 μA/off mode (RAM retention); port line input leakage current is less than 50 nA.
    MSP430 series development tools are convenient and advanced. This paper conducts ultra-low power consumption research based on MSP430G2553 model microcontroller. The relevant experiments use MSP430 LaunchPad development board, whose microcontroller uses 20-pin PDIP package, and the compilation tool uses Code Composer Studio v5.1.1. The software programming uses C language.

2 MSP430G2553 microcontroller ultra-low power consumption design principles
    MSP430 series microcontrollers are representatives of ultra-low power microcontrollers. It has a flexible clock system, multiple deep low power modes, and highly automated intelligent peripherals. It makes full use of the characteristics and internal modules of MSP 430G2553 to achieve ideal low power consumption characteristics.

    Figure 1 shows a typical low-power system CPU operation mode. The system is idle most of the time, and only processes some tasks when an event occurs or is scheduled. The power consumption of the entire system is equal to the area under the average value curve. Reducing system power consumption means selecting a low-power mode when idle and minimizing work consumption when running. [page]

2.1 Idle state
    Many low-power systems consume more than 80% of their energy in idle state, so deep sleep mode should be selected as much as possible in idle state. MSP430 series microcontrollers provide multiple working modes, as listed in Table 1, which can flexibly control the system clock and auxiliary clock.

   Generally, the method of maximizing LPM3 time is adopted to minimize power consumption. The MSP430 series microcontroller can quickly and conveniently switch working modes. Through interrupts, the CPU can be awakened from low power mode within 6μs to control the program flow. Due to the fast CPU processing speed and short exit time from low power consumption, the CPU can be kept idle most of the time, reducing the power consumption of the microcontroller system.
2.2 Running state
    The power consumption of the CMOS digital system in the running state can be calculated by formula (1):
   
    Where: P is the power of the CMOS digital system in the running state, C is the load capacitance of CMOS, f is the clock frequency of the system, and Vcc is the power supply voltage.
    It can be seen that the power supply voltage has the greatest impact on the power consumption of the system, followed by the clock frequency, and then the load capacitance. For users, the load capacitance is generally uncontrollable. Therefore, to design a low-power microcontroller system, there are two main principles: reduce the power supply voltage as much as possible; reduce the clock frequency as much as possible. Other methods are basically implemented around these two principles. The power supply voltage and clock frequency are shown in Figure 2.

2.2.1 Power supply voltage
    The higher the power supply voltage is at the same main frequency, the higher the power consumption is. It is necessary to design a reasonable power supply system and flexibly adjust the core voltage of the microcontroller to reduce power consumption. The typical values ​​of Vcc and Icc under AM are listed in Table 2. In active mode (AM), the power supply current (Icc) of the MSP430G2553 microcontroller changes with the power supply voltage (Vcc).

2.2.2 Clock frequency
    The clock system of MSP430G2553 is specially designed for battery power supply. MSP430G2553 microcontroller has different clock sources, which generate 3 adjustable clock frequencies: low-frequency auxiliary clock (ACLK), high-frequency main system clock (MCLK) and high-frequency subsystem clock (SMCLK). The frequencies of the three clocks are weighed according to the actual needs of each peripheral module, the highest requirements for processor speed and clock accuracy. For some low-frequency peripherals, ACLK can be used as the clock or signal source instead of MCLK, so as to reduce power consumption; whether for CPU or external devices, the operating frequency should be reduced as much as possible, and automatic shutdown can be designed when it does not affect the function.
2.2.3 I/O port
    For ordinary I/O ports, it is necessary to configure them in output mode to avoid the influence of external floating voltage. There should be no floating pins on the CMOS input end, and all input ends should be connected to appropriate levels.

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2.2.4 External devices
    Configure the appropriate working mode for the on-chip external devices and perform appropriate power consumption management for the external devices in the system to reduce power consumption and CPU usage. In specific applications, it is recommended to disable all unused peripheral modules, and use ADC converters with enable pins and op amps with enable pins.
2.2.5 Intelligent peripherals
    Make full use of the intelligent peripherals of MSP430G2553 so that it can work independently of the CPU and keep the system in low-power mode for a longer time. For example, ADC10 can realize automatic polling sampling of multiple channels and can realize automatic transfer of ADC conversion results. By properly configuring registers, the CPU load can be reduced to a minimum, thereby achieving the purpose of reducing power consumption.
2.2.6 Other
    DMA linkage with other peripherals, timer automatic triggering of ADC and other functions can realize intelligent operation between different modules on the chip and reduce system power consumption.
2.3 Software programming
    The simplicity of software design is directly related to the time required for the CPU to complete the task. MSP430G2553 has a unified addressing space, a completely orthogonal instruction system and sufficient general registers, which can ensure the high efficiency of C language compilation. But at the same time, in system design, software engineers are required to design the most concise code, with the following points:
    ① Try to use local variables, which are usually assigned to general registers and have high instruction efficiency;
    ② Try to use unsigned numbers;
    ③ Use pointers to address structures and unions;
    ④ Decrement the counter when using the fox loop;
    ⑤ Try to use fast table lookup instead of algorithm calculation, and try to use calculation branches instead of testing flags, etc.

Conclusion
    By selecting MSP430G2553 microcontroller and configuring it reasonably, the optimal power consumption design of the system can be achieved. MSP430G2553 microcontroller has good application prospects in portable instruments, intelligent sensors, measurement and control equipment and other fields, which is in line with the theme of "green environmental protection and sustainable development".