The MSP430 family of microcontrollers is a 16-bit ultra low power hybrid microcontroller with a reduced instruction set. One of the biggest advantages of using the MSP430 family of microcontrollers is its low power consumption and high integration, making it ideal for battery-powered and space-constrained work environments as well as portable applications.
1 MSP430 series MCU low power principle and working mode
1.1 Low power principle
The MSP430 family of microcontrollers has very low power consumption and is determined by its structural characteristics.
1.1.1 Flexible clock signal
The MSP430 series MCU provides different clock signals for the system, and the user can select the appropriate system clock according to actual needs. The clock module of MSP430 is composed of high-speed crystal oscillator, low-speed crystal oscillator, digitally controlled oscillator DCO, frequency-locked loop FLL and frequency-locked loop enhanced version FLL+. The MSP430 family of microcontrollers outputs three different clock signals: ACLK (auxiliary clock), MCLK (main system clock), and SMCLK (subsystem clock). The following takes the clock module of the MSP430F4XX series MCU as an example.
The clock module of MSP430F4XX series MCU has three clock sources: LFXT1CLK, XT2CLK, DCOCLK. LFXT1CLK is a low frequency clock; XT2CLK is a high frequency clock; DCOCLK is an on-chip digitally controlled RC oscillator that is often used as a clock signal for systems and peripherals, and its stability can be controlled by FLL+ hardware.
The structure of the MSP430F4XX series MCU clock module is shown in Figure 1. ACLK is from LFXT1CLK and can be selected as the clock signal of each peripheral module by software. It is generally used for low-speed peripherals. ACLK is divided by 1, 2, 4, and 8 for external circuit, which ensures the compatibility of MSP430F4XX and MSP430F1XX clock systems. MCLK can be selected by software from one of LFXT1CLK, XT2CLK, DCOC-LK, and then divided by 1, 2, 4, 8 frequency, mainly used for CPU and system; SMCLK can be selected by software from XT2CLK or DCOCLK, mainly for high speed Peripheral module. According to different application requirements and system conditions, the user selects low frequency or high frequency through the program, and three different frequency clocks are output to different modules, so that the voltage of the system is utilized reasonably, and the low power consumption of the whole system is realized.
DCOCLK can be used as MCLK and SMCLK, but since the frequency of the RC oscillator DCO varies with temperature and voltage, the output frequency is unstable. The clock module of MSP430F4XX series MCU uses the enhanced frequency-locked loop technology FLL+. The frequency of the DCOCLK can be stabilized by the automatic adjustment of the frequency integrator and the modulator, and the hardware automatically adjusts the DCO frequency. The clock module of the MSP430F1XX series MCU is realized. The DCO frequency needs to be adjusted by software.
1.1.2 Peripheral modules that operate completely independently
Each module of the MSP430 series MCU runs completely independently, and the timer and A/D converter can operate independently while the CPU is in a sleep state, thereby reducing the power consumption during system operation. For example, the output of a square wave is implemented in two ways.
Mode 1 is a way that is usually used by a single-chip microcomputer. The CPU controls the output port to achieve high- and low-level alternate conversion. In this way, the CPU is always working. The procedure for Mode 1 is as follows:
Mode 2 uses the automatic flip mode of the MSP430 external module timer A1 to achieve high and low transitions. In this way, after setting the operating mode of timer A1, the CPU controls the waveform by the output of timer A1. The CPU can be dormant without any CPU involvement, which reduces the power consumption of the system. The procedure for mode 2 is as follows:
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